fixed typo in comment

This mistake was a bit confusing, so I thought it was worth sending a PR over.

Comments:
_The documentation is not available anymore as the PR was closed or merged._

<details>
<summary>Show benchmarks</summary>

PyArrow==8.0.0

<details>
<summary>Show updated benchmarks!</summary>

### Benchmark: benchmark_array_xd.json

| metric | read_batch_formatted_as_numpy after write_array2d | read_batch_formatted_as_numpy after write_flattened_sequence | read_batch_formatted_as_numpy after write_nested_sequence | read_batch_unformated after write_array2d | read_batch_unformated after write_flattened_sequence | read_batch_unformated after write_nested_sequence | read_col_formatted_as_numpy after write_array2d | read_col_formatted_as_numpy after write_flattened_sequence | read_col_formatted_as_numpy after write_nested_sequence | read_col_unformated after write_array2d | read_col_unformated after write_flattened_sequence | read_col_unformated after write_nested_sequence | read_formatted_as_numpy after write_array2d | read_formatted_as_numpy after write_flattened_sequence | read_formatted_as_numpy after write_nested_sequence | read_unformated after write_array2d | read_unformated after write_flattened_sequence | read_unformated after write_nested_sequence | write_array2d | write_flattened_sequence | write_nested_sequence |
|--------|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 0.005855 / 0.011353 (-0.005498) | 0.003556 / 0.011008 (-0.007452) | 0.079430 / 0.038508 (0.040922) | 0.056754 / 0.023109 (0.033645) | 0.311718 / 0.275898 (0.035820) | 0.346731 / 0.323480 (0.023251) | 0.004414 / 0.007986 (-0.003571) | 0.002835 / 0.004328 (-0.001493) | 0.062138 / 0.004250 (0.057888) | 0.044259 / 0.037052 (0.007206) | 0.314681 / 0.258489 (0.056192) | 0.359802 / 0.293841 (0.065961) | 0.026684 / 0.128546 (-0.101862) | 0.008023 / 0.075646 (-0.067623) | 0.260148 / 0.419271 (-0.159123) | 0.043734 / 0.043533 (0.000202) | 0.312081 / 0.255139 (0.056942) | 0.340004 / 0.283200 (0.056805) | 0.019559 / 0.141683 (-0.122124) | 1.488758 / 1.452155 (0.036604) | 1.510828 / 1.492716 (0.018111) |

### Benchmark: benchmark_getitem\_100B.json

| metric | get_batch_of\_1024\_random_rows | get_batch_of\_1024\_rows | get_first_row | get_last_row |
|--------|---|---|---|---|
| new / old (diff) | 0.181376 / 0.018006 (0.163370) | 0.441726 / 0.000490 (0.441236) | 0.001722 / 0.000200 (0.001522) | 0.000066 / 0.000054 (0.000012) |

### Benchmark: benchmark_indices_mapping.json

| metric | select | shard | shuffle | sort | train_test_split |
|--------|---|---|---|---|---|
| new / old (diff) | 0.023760 / 0.037411 (-0.013651) | 0.071847 / 0.014526 (0.057321) | 0.082642 / 0.176557 (-0.093915) | 0.145555 / 0.737135 (-0.591580) | 0.084554 / 0.296338 (-0.211784) |

### Benchmark: benchmark_iterating.json

| metric | read 5000 | read 50000 | read_batch 50000 10 | read_batch 50000 100 | read_batch 50000 1000 | read_formatted numpy 5000 | read_formatted pandas 5000 | read_formatted tensorflow 5000 | read_formatted torch 5000 | read_formatted_batch numpy 5000 10 | read_formatted_batch numpy 5000 1000 | shuffled read 5000 | shuffled read 50000 | shuffled read_batch 50000 10 | shuffled read_batch 50000 100 | shuffled read_batch 50000 1000 | shuffled read_formatted numpy 5000 | shuffled read_formatted_batch numpy 5000 10 | shuffled read_formatted_batch numpy 5000 1000 |
|--------|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 0.401688 / 0.215209 (0.186479) | 4.000994 / 2.077655 (1.923339) | 2.047109 / 1.504120 (0.542989) | 1.891874 / 1.541195 (0.350679) | 1.970599 / 1.468490 (0.502109) | 0.500646 / 4.584777 (-4.084131) | 3.006623 / 3.745712 (-0.739089) | 4.248359 / 5.269862 (-1.021503) | 2.613946 / 4.565676 (-1.951730) | 0.057921 / 0.424275 (-0.366354) | 0.006407 / 0.007607 (-0.001200) | 0.470676 / 0.226044 (0.244631) | 4.722280 / 2.268929 (2.453352) | 2.448530 / 55.444624 (-52.996095) | 2.175841 / 6.876477 (-4.700635) | 2.352287 / 2.142072 (0.210214) | 0.589049 / 4.805227 (-4.216179) | 0.125145 / 6.500664 (-6.375519) | 0.060829 / 0.075469 (-0.014640) |

### Benchmark: benchmark_map_filter.json

| metric | filter | map fast-tokenizer batched | map identity | map identity batched | map no-op batched | map no-op batched numpy | map no-op batched pandas | map no-op batched pytorch | map no-op batched tensorflow |
|--------|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 1.189225 / 1.841788 (-0.652563) | 16.753085 / 8.074308 (8.678777) | 13.086512 / 10.191392 (2.895120) | 0.132371 / 0.680424 (-0.548052) | 0.016933 / 0.534201 (-0.517268) | 0.328258 / 0.579283 (-0.251025) | 0.344074 / 0.434364 (-0.090290) | 0.374042 / 0.540337 (-0.166296) | 0.515307 / 1.386936 (-0.871629) |

</details>
PyArrow==latest

<details>
<summary>Show updated benchmarks!</summary>

### Benchmark: benchmark_array_xd.json

| metric | read_batch_formatted_as_numpy after write_array2d | read_batch_formatted_as_numpy after write_flattened_sequence | read_batch_formatted_as_numpy after write_nested_sequence | read_batch_unformated after write_array2d | read_batch_unformated after write_flattened_sequence | read_batch_unformated after write_nested_sequence | read_col_formatted_as_numpy after write_array2d | read_col_formatted_as_numpy after write_flattened_sequence | read_col_formatted_as_numpy after write_nested_sequence | read_col_unformated after write_array2d | read_col_unformated after write_flattened_sequence | read_col_unformated after write_nested_sequence | read_formatted_as_numpy after write_array2d | read_formatted_as_numpy after write_flattened_sequence | read_formatted_as_numpy after write_nested_sequence | read_unformated after write_array2d | read_unformated after write_flattened_sequence | read_unformated after write_nested_sequence | write_array2d | write_flattened_sequence | write_nested_sequence |
|--------|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 0.005963 / 0.011353 (-0.005390) | 0.003484 / 0.011008 (-0.007525) | 0.062618 / 0.038508 (0.024110) | 0.057217 / 0.023109 (0.034108) | 0.426760 / 0.275898 (0.150862) | 0.464422 / 0.323480 (0.140942) | 0.005276 / 0.007986 (-0.002709) | 0.002872 / 0.004328 (-0.001456) | 0.062636 / 0.004250 (0.058385) | 0.045953 / 0.037052 (0.008900) | 0.433221 / 0.258489 (0.174732) | 0.475087 / 0.293841 (0.181246) | 0.027217 / 0.128546 (-0.101329) | 0.007965 / 0.075646 (-0.067681) | 0.067749 / 0.419271 (-0.351522) | 0.041235 / 0.043533 (-0.002298) | 0.425424 / 0.255139 (0.170285) | 0.453390 / 0.283200 (0.170190) | 0.020217 / 0.141683 (-0.121466) | 1.436354 / 1.452155 (-0.015801) | 1.492372 / 1.492716 (-0.000345) |

### Benchmark: benchmark_getitem\_100B.json

| metric | get_batch_of\_1024\_random_rows | get_batch_of\_1024\_rows | get_first_row | get_last_row |
|--------|---|---|---|---|
| new / old (diff) | 0.226896 / 0.018006 (0.208889) | 0.411935 / 0.000490 (0.411445) | 0.000356 / 0.000200 (0.000156) | 0.000054 / 0.000054 (-0.000000) |

### Benchmark: benchmark_indices_mapping.json

| metric | select | shard | shuffle | sort | train_test_split |
|--------|---|---|---|---|---|
| new / old (diff) | 0.024705 / 0.037411 (-0.012706) | 0.076232 / 0.014526 (0.061706) | 0.086949 / 0.176557 (-0.089608) | 0.141867 / 0.737135 (-0.595269) | 0.088199 / 0.296338 (-0.208140) |

### Benchmark: benchmark_iterating.json

| metric | read 5000 | read 50000 | read_batch 50000 10 | read_batch 50000 100 | read_batch 50000 1000 | read_formatted numpy 5000 | read_formatted pandas 5000 | read_formatted tensorflow 5000 | read_formatted torch 5000 | read_formatted_batch numpy 5000 10 | read_formatted_batch numpy 5000 1000 | shuffled read 5000 | shuffled read 50000 | shuffled read_batch 50000 10 | shuffled read_batch 50000 100 | shuffled read_batch 50000 1000 | shuffled read_formatted numpy 5000 | shuffled read_formatted_batch numpy 5000 10 | shuffled read_formatted_batch numpy 5000 1000 |
|--------|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 0.419748 / 0.215209 (0.204539) | 4.198597 / 2.077655 (2.120942) | 2.338477 / 1.504120 (0.834357) | 2.195741 / 1.541195 (0.654547) | 2.278145 / 1.468490 (0.809655) | 0.502365 / 4.584777 (-4.082412) | 2.987773 / 3.745712 (-0.757939) | 2.896526 / 5.269862 (-2.373336) | 1.841610 / 4.565676 (-2.724067) | 0.058032 / 0.424275 (-0.366243) | 0.006470 / 0.007607 (-0.001137) | 0.496969 / 0.226044 (0.270925) | 4.960984 / 2.268929 (2.692056) | 2.648615 / 55.444624 (-52.796009) | 2.286846 / 6.876477 (-4.589631) | 2.320176 / 2.142072 (0.178104) | 0.600550 / 4.805227 (-4.204678) | 0.125652 / 6.500664 (-6.375012) | 0.062177 / 0.075469 (-0.013292) |

### Benchmark: benchmark_map_filter.json

| metric | filter | map fast-tokenizer batched | map identity | map identity batched | map no-op batched | map no-op batched numpy | map no-op batched pandas | map no-op batched pytorch | map no-op batched tensorflow |
|--------|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 1.293063 / 1.841788 (-0.548725) | 18.294204 / 8.074308 (10.219896) | 13.720502 / 10.191392 (3.529110) | 0.146480 / 0.680424 (-0.533944) | 0.016965 / 0.534201 (-0.517236) | 0.330137 / 0.579283 (-0.249146) | 0.352051 / 0.434364 (-0.082313) | 0.381754 / 0.540337 (-0.158584) | 0.517935 / 1.386936 (-0.869001) |

</details>
</details>

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