It is unusual in several aspects:
- The first day of transcript shows similar messages which are shown in the "main" chatroom - many sites have a room that was created together with creation of the site. ("Welcome to chat for: Mathematics This is a general discussion room, but please feel free to create more subject-specific rooms (a single room with every possible discussion isn't very helpful). For playing with chat features Sandbox...") However, there are much older rooms associated with this site, including the one which the most users of Mathematics Stack Exchange use.
- It seems that the room was never frozen, but it had no activity between August 2017 and May 2020. (According to the chat FAQ, a room is frozen after 14 days of inactivity; while several posts here on meta mention that one exception is that if the room is the sole room for a particular parent site, it isn't frozen, this isn't the case here.)
- The logo in the room info says "Mathematics". But when I list the rooms associated with Mathematics Stack Exchange and sort them by recent activity, I do not see this room in the list.
Question. Why wasn't this chatroom frozen? Which site is it associated with?
I am asking partly out of curiosity. And partly because sometimes it might be useful to have a room which can never be frozen.
EDIT: Some other instances of sites that have two "main" chat rooms, one of them inactive:
- Christianity: 2011 and 2014
- Role-playing Games: 2010, 2014
- Seasoned Advice: 2010, 2015
- Wordpress Development: 2010, 2014. (The latter was manually frozen by a moderator.)
- Ask Ubuntu: 2012, 2015
- Super User: 2011, 2015 (This one was manually frozen and deleted by mods after this question was posted.)
- ServerFault: 2010, 2015
EDIT2: Mithical's answer explains that this room is actually associated with chat.math.stackexchange.com. Sonic the Anonymous Hedgehog has created another room associated with chat.math.stackexchange.com. And the room mentioned above was eventually frozen.