Saying "self-verified" is massively downplaying it. They are formalized and checked in Lean4 1, which is a programming language used by mathematicians today, to mechanically check their proofs to rule out human error. In other words a theory being stated in Lean generally means it's more likely to be correct than one stated in mere human language.

Now, Lean, like any piece of software, has had bugs. A while back someone exploited a Lean bug to "prove" the Collatz conjecture 2. So it is possible that AI agents found a bug and used it. But the vibes I got from mathematicians in the field is that that's not very likely.