The contrast tells us "the right side is obviously stylized, and this illustrates that the left side is rendered with realistic perspective".

Which means the rock is round and proves the authors incorrect because they overlook this obvious perspective to claim the rock is flat and axe-like to make their comparison. Their theory rests entirely on the rock in the painting being flat, which could only be true if the perspective was flat. The painter made sure we can see that is not the case.

The painter is telling us there is a narrative and a reality. They baby appears unconvinced and suspicious, as if he knows there is an alternate truth to the story. He appears to be pointing at rock. The baby is telling us he is not the subject, the rock is.