I really don't think he sees his reflection. He can still see me moving in the darkened room so I know he can see at least partially through to the room, and he goes crazy chasing the other fish in the tank. You'd think he'd just flare and attack the glass if it was a reflection.
I try to not turn the room lights out with the tank light on because he hits the glass hard enough I can hear it, can't be good for him.