Why not? I do think the girl was overreacting and the threat was unnecessary (although I wouldn't be surprised if she was just empty threatening him in order to provoke a faster response), but we are adults in a professional school who will be physicians in a few years. OP took on the responsibility of the group, didn't put in the required effort to keep it going, and avoided responding to the person who wants to take it over and bring it back. IMO if you take on the responsibility of a group, even if it's a "meaningless" student group, you have a professional obligation to either actually fulfill your responsibilities or pass it on to someone more capable. Maybe it's not a professional obligation to another student, it's more of a professional obligation to the school-associated student group. He was also responsible for some material associated with the group, which belonged to the group, not to him, which he left in his locker and is most likely in the trash now. In the big scheme of things, these little things probably don't matter, but you have to wonder what OP will do when he has real responsibilities.
And I would agree if this were the only instance of him avoiding emails. A fellow med student reporting him about a club would not make it into the MSPE. But there is clearly a general professionalism concern as this has happened at least twice now. OP still has another year before that gets written, so if he continues this trajectory, it could definitely be a problem.
Also, not every student group has a faculty advisor who knows what's going on. You usually have a faculty advisor listed, but that's just for the paperwork. Often the students run the show. And if the girl contacted the faculty member who in turn contacted OP, and OP continued avoiding the emails, then THAT would be an even bigger professionalism problem.