Magnus would have answered Alec's question. He would have explained that he still has a personality, wants and desires that don't have anything to do with sex. (...Sort of.) He would have made it clear that he's capable, to an extent, of friendship and niceties, conversation and connection.

But then Alec had to go and ruin it with that parting comment.

Magnus' eyes went flinty and he pulled his hand away from Alec. He wouldn't kill him, but there was definitely something hard and... disappointed in his gaze.

"You keep saying that you don't know how this works, but you seem very certain in what you know about me."