[Oh boy, that wasn't a reaction he had expected...! But he's pretty fast when it comes to reciprocating emotions, and the enthusiasm is reflected at least in part.]

Oh! Isn't that a coincidence? [One that kind of makes him wonder if there's a rhyme or reason to the housing assignments after all, but he'll save that thought for later.]

I have to admit that it's a relief to share living space with such an agreeable person. Having clashing motives would make things a little awkward, I'd imagine.