I'm a research mathematician, and to me the biggest surprise is that the user didn't identify themselves or (yet) try to claim credit for their work.
Within academia, it is to your definite advantage to have your name associated with breakthroughs, for obvious reasons. Outside academia I don't have firsthand experience, but I'd have to imagine the same holds.
It is also a sign of wisdom and maturity to not care so much, especially outside academia.
I know your reaction is the normal one these days, but I’d like to normalize the ones that don’t care about society petting them on the head and saying atta boy. They just deliver the work and retreat into the darkness. I find it highly inspiring. The alternative.. not so much.
If this work has an implication for cryptography they might want to be anonymous for any number of reasons.
Update: the linked page has now been updated to say:
> it was Claude, with Levent Alpöge and Ava Howell!
Alpöge is the same guy who prompted Claude for a proof of the Jacobian conjecture.