Maybe he too is a dragon
I had that thought too. Like maybe he doesn't have horns because of something concerning the unspoken incident or maybe something connected to 'that guy' from his memories (who is probably his dad or something), or maybe even he just hides them with magic but then he didn't have horns in flashbacks. Not even as a kid before regaining memories. He is not werewolf, vampire, succubus, fairy, centaur, giant, slime, goblin, skeleton, Harpy, spirit animal (I think those are all races mentioned until now?) so that would mean he'd be a dragon or unmentioned yet race. Maybe he is half dragon and that's why he doesn't have horns though. Maybe that makes him a hybrid and something and that's another reason magicians are this way to him? Although they probably just wish they had his magic.
Oh, so he’s not human (⊙…⊙ )