I don't think we should be Draconian about policing this. I think the policy should be no posting music composed by AI, but I really think it would be a mistake to start policing and interrogating every post and assuming it's AI until proven otherwise. If there are indications that a piece might be AI (e.g. no score provided, telltale signs of Sonus, posted by someone with no prior history on the forum, etc.), then it makes sense to inquire further into it. But demanding proof of authorship from every composition would be a drastic overreaction to an issue that has, as far as I'm aware, only actually cropped up once here so far.
I'm against AI compositions on the forum, but I'd rather waste my time once or twice giving useless feedback on an AI composition than chase real people who are posting real compositions off the site.