You're acting like the brain is some kind of simple algorithm, more goes into a painting or a composition than just a bit of simple logic. A composer is not sitting there at 2am on her Piano going "Hm, I like round numbers, so I might make this note a F because it's the fourth note in the C major scale".
I might be wrong but from my understanding, we don't even really understand how neural nets are able to make certain decisions or generate certain pictures yet, correct?