I mean, it could make sense in a matter of "i wanted to have a way of having more time with MC" but character wise he doesn't seem like the kind of people who could lie to his old friend, still the fact MC refused to have a shared room with Mikko would make Mikko have an actual reason to do so, we'll probably discover about it later. But the hug isn't it for sure because if you sit with lake Mikko won't be able to hug you
Mikko could also have seen MC's keys falling at any point (either before, during or after the hug if you sit with him) and could have seen the perfect chance to take them, considering that:
-he's the only with an actually concrete motive
-he's the only that know MC well except for lake, the others would have given it to devon as they just met MC and so they wouldn't recognize his key
Edit: :0 Mikko hug you even if you don't sit with him, he does so before you loose your key, Mikko is getting some suspicious on him