Aaaaaand cue the smitten ninja!

Truth be told there is a bit of logic to it, The short of it is he has always had a shifted view of what is acceptable, from examples such as magneto's constant cultivation of mutants even if they have no powers beyond mere physical disfigurements to live in genoshia to Nightrawlers constant oppression against his physical appearance. These have lead him to twist his views that only the physically disfigured or those unable to turn off their powers are beautiful. So far everyone has pretty much been playing 'pretty' mutants as the morloks would call them, those who are baseline humans with powers beyond that. 

With their powers under control, 90% of them look just like anyone else and Magnus hates that. It makes him feel like an outsider amongst outsiders since he can never turn off being blue or having a tail. Now here comes a girl who cant stop being a human nightlight awake or asleep. Yep, he's gone.

Mind you, this is a 'first sight' thing and once he gets to know her he will shift his opinions of her. But for the moment, he's all over her.