That makes sense now knowing it was a threaded conversation. I agree with you now, it was entirely reasonable - especially given the main chat had continued outside the thread. Don't know about you but I find threaded chats more annoying than useful, even on Slack with it's better UX. It feels like the IM equivalent of when you're having a meeting and 2 people start having their own separate conversation, making it harder to follow what's going on.