I think humans do in fact create things out of 'thin air' - but only in very, very small pieces. What we consider to be an absolute genius is typically a person who has made one small original thought and applied it to what already exists to make something different.

Creating something novel is not even remotely the same as creating something out of thin air. Even the genius with an original thought only could come by that thought by being informed through their life experiences. Not unlike an AI training set allowing an AI to create something novel.

Is creation coming about by analysis of life experience somehow different from creation coming about by analysis of training data?

Yes, because it's multimodal, and because you can think of new things to look at and go out in the world to look at them.

Humans have access to much better thinking abilities than art AIs do.

e.g. SD2 prompted with "not a cat" produces a cat, and "1 + 1" doesn't produce "2".

Some stable diffusion interfaces let you specify a "negative input" which will bias results away from it. It wouldn't be terribly hard to do some semantic interpretation prior to submission to the model that would turn "not a <thing>" into "negate-input <thing>"