As of November, anyone making a game or asset is asked to report whether they're using AI or not; it's also retroactive for stuff that's previously been released. (That doesn't mean that everyone has answered. Supposedly after a grace period, you'll be able to report untagged AI stuff, but it's been four and a half months. It also doesn't guarantee people telling the truth, but.) The No AI works to search for people who said no to the question.
The disclosure isn't something you can check on the page itself, though--it affects searches and only searches. (Itch should really fix that.) If you see the tag, it's because the person who submitted it added it manually.