I don't see what the big deal is here. Maybe it wasn't handled the best way, but since the thread was not closed for violation of the rules, there is nothing stopping someone from starting a new thread, linking to the closed one in the first post and continuing the conversation. To me that is equivalent to the idea of taking the conversation outside. Maybe thread starters should "leave the room" instead of making everyone leave, but again they can't stop everyone else from continuing somewhere else.
Part of this particular case to me is that the tone had dropped from being completely civil (at least one other poster felt the thread was going to be closed soon) and the thread starter may have felt partially responsible for that so asked it be closed before it got out of hand and was forced closed by the moderators.