At times, some of my human-written content is picked up by AI detectors as having some probability of being written by AI (less than 30%), if I take the time to focus on style, tone, audience, etc.
I don't think we can rely on detectors to tell us the full truth. Only the AI that generated it knows whether it's AI or not.
If you got one of the top English writers here to write one paragraph about the best dog food, I would almost guarantee that it would be picked up as written by AI with some probability, if not all.
That said, I don't know how Google is going to handle AI content when it comes to forums. Is it just going to scan it for correctness and ignore that it wasn't written by a human? That seems the most logical. Serve up the most correct and most concise content a user is looking for.