"Engineered."

I occasionally forget--but not for long--that the High Evolutionary is not a benign figure. He did some frankly, evil stuff during the Evolutionary War: he sterilized a lot of Moloids in like the first chapter alone. He's also, in Kurt's case, kind of like the fertility specialist that helped your parents conceive, showing up decades later for some appreciation like he was the third parent or some goddamn thing. Sat is right, he is a creepy dude: just because he has a little more bearing than say, MODOK or Arnim Zola, doesn't make him a good guy. 

 Kurt doesn't even spend that much time with either Azazel or Mystique; but I guarantee he has heard the details of his conception in Penthouse Forum level detail from both of them. I think Kurt's more comfortable with sex than some X-types (or how he was written in Way of X) but Azazel and Mystique probably consider him 'square' and easily shocked. And like most senior X-Men, Kurt is completely unphased by weird earth-shattering revelations from his past: secret siblings, parent reveals, kids from alternate timelines, the occasional clone. He's seen it.