Right? It's baffling.

The title is specifically referring to a possible reassessment of his later, quasi-mystical writings, post retirement from mathematics in 1970.

It’s a bit too long for the HN title submission but the actual article title in the Guardian is

“ ‘He was in mystic delirium’: was this hermit mathematician a forgotten genius whose ideas could transform AI – or a lonely madman?”

Why not both? Crazy people can be smart. As for mystic delirium well that's our modern sensibilities talking. Hell there are people today who believe in Marian apparitions.

Wasn't Newton a mystic too? Yes, he was [1].

[1] https://en.wikipedia.org/wiki/Isaac_Newton%27s_occult_studie...

He left IHÉS around 1970 but he stayed active in math, and he kept working as a math professor and later at the CNRS (French research institute).

https://en.wikipedia.org/wiki/Alexander_Grothendieck#Manuscr...