I think what happened is that this artist was painting from his imagination, and he painted that boy with the blue pants that you can see at the bottom of the painting first.

But he really fucked up that part and the blue pants boy looked super weird, and he couldn't figure out how to fix it, so he painted another boy on top of the first boy to hide the mistakes.

But then, that boy looked pretty weird, too, so he painted a horse on top of the boy. But he painted the horse too small, so he had to have the horse lift its leg to hide at least part of the boy. But then, the horse looked pretty weird itself, so he just moved to a different part of the painting.