That room is titled "room-between-hyperneutrino-and-sr-4der", it's more private than (for example) this room:
chat.stackexchange.com/rooms/100450/physics - assuming that new account isn't deleted, as the moderator suggested that they are inclined to do, then they should be able to request access (much as you could do in the second link above). The first room is hidden and private, the second isn't hidden but access to post comments can be requested. The third type of room is open.