I'm curious about how those rules work. It's always about "AI Art", but I don't think that's an accurate term. People could stylize their game with neural style transfer, and that would get flagged under the rule, even though it's possible to explicitly provide credit. Furthermore, there are models trained on only datasets consisting of natural images (though most of those used in practice have copyright issues); I don't see how that puts artists' work at risk of being stolen.
You're right, it should probably be more comprehensive that just "AI Artwork" so we will also be including voice overs and writing in this. If somehow you and every other person submitting a game could come up with a way to prove that their AI artwork, voice overs, and writing was not trained using/based off of other people's work, then we will happily change the rules.
However, we are not here to argue the ethics of AI materials. We've made a decision we are comfortable with, and we will be sticking with it.