There would be a real question if the judge in fact used AI. The plaintiff's complaint (https://storage.courtlistener.com/recap/gov.uscourts.nvd.176...) makes it pretty clear that he's just nuts and had no real reason to think she did.

But of course a court can't dismiss someone's complaint on the grounds that they're nuts; in order to rule on the substance of this case, a court would have to conduct new hearings to gather all the details about the original hearing in which AI was allegedly used. The purpose of judicial immunity is to push all objections to judicial decisions through the appellate courts, which don't have to re-hear everything before issuing a ruling.