He might also be reading about EDs amongst fat people and trying to broach the subject. Not saying he assumes you have an ED but perhaps is suspicious for some reason and just trying to get more info. Plenty of fat people have EDs, including anorexia and it's because of anti-fatness that society in general doesn't realize this or refuses to accept it. But, yes, it's a bit odd if it came out of the blue like that with no push from you.