As other comments have pointed out, this article is inaccurate — particularly about root causes. It's frustrating in part because it is so easy to tell it's not true: look at anything "blue" and notice that it's not blurred. There are a few operating principles here that explain why this observation is functionally incorrect, but also how it's adjacent to the truth.

The first is metamerism, or more generally the fact that we don't observe wavelength directly. Many of the blue colors we can perceive in the real world have a lot of "green" and "red" wavelengths in them too; the cones that detect green and red will still fire for those collections of wavelengths, but the blue-detecting cones will fire faster. We perceive "blue" through higher level processing of those signals; furthermore, it's not a 1:1 mapping.

More importantly: most light we see isn't spectrally pure, so chromatic aberration is not as significant as those charts seem to indicate; rather than multiple distinct planes of good focus, you really have a general region that has a minimum spot size. For most human eyes that spot size is pretty small; errors in the human eye are going to be a larger factor than chromatic aberration for most people.

Also significant: most chromatic aberration people talk about in lenses is lateral chromatic aberration, which can be significant in biological eyes — it's supposedly why herbivores with wide fields of view have horizontal irises! — but for human color vision, most of our acuity is in the foveal region, for which LCA is vanishingly small. The magnitude of LCA is a function of angular distance from the chief ray (~foveal). Axial chromatic aberration has a much smaller effect and generally only affects your minimum spot size, but as mentioned before biological eyes are not accurate enough for this effect to dominate.

Now, what the article nearly gets right: there are examples of light you can't focus on: short wavelength light that is spectrally pure (and sufficiently distant) could be 'unfocusable' for certain eyes. I can report with high confidence this is true for my eyes, and likely for a lot of other people. You can see this with blue laser light, some violet-hued LEDs (not red + blue mixed), or even the visible spectrum from mostly-UV sources. I find that the light itself will appear to have a halo and not be particularly sharp; for me, the perceptual effect is not quite like it being blurry, because the shape of the 'blur' is affected by my eye's aberrations, so it tends to have a 'spiky' bokeh. YMMV.

Finally, there is a truth about human color vision that the tests here seem to get close to: we mostly perceive sharpness or acuity in images as a function of luminance, not chrominance. (Modern image and video formats exploit this extensively.) In fact, the equation to derive luminance from chrominance values models this explicitly; it varies based on color space, but here's the equation for sRGB:

Y = 0.2126R + 0.71522G + 0.0722B

Where Y is luminance, and R, G, and B are the individual color channel values (source: https://en.wikipedia.org/wiki/Relative_luminance). Note the coefficient for blue suggests that only ~7% of our brightness perception derives from the blue channel. This is the source of chroma-based data compression, where we throw away data in the chrominance channels but maintain it in luminance (see YCrCb coding), which is also the reason why blue seems to matter less when doing per-channel blurring: it simply contributes less to the perceived luminance value due to the mechanics of human color perception.