This is an odd, pathetic, stupid decision from Valve.
One of the best use cases for AI in its current state is that it can automate making some of the art assets in a video game so a smaller team can make something ambitious. But arbitrary rage of Luddites sadly disallows this.
Another steam game rejected for "AI" except they didnt use AI. If valve even has the suspicion of you using AI, they will reject.
Can you even really tell if somethings made by AI 100% of the time?