Place the jars near a window. After several days observe what has happened in each jar. The bread dough and salt provided food for the mould. They are even flying around in the air, but since they are so incredibly small, our eyes can't see them. More mould probably grew on the bread dough with the dirt on it.
Dirt acts like glue, and catches mould spores.
There were more mould spores on the dirty bread dough than the clean bread dough, so more mould grew on the dirty bread dough. Mould like the warmth. The sun shining through the window probably provided extra warmth for the mould to grow. Mould likes moisture. By closing the lid of the jar, the moisture gets trapped inside the jar providing the perfect environment for the mould to grow.