A conference always runs in a browser tab of its own — the chat has no window for one. The card posted in the channel is the door, and the only one: Group Call in the conversation's toolbar opens the room and writes that card rather than going anywhere itself. The call gets the whole window and the conversation stays where it was.
Closing the tab is not leaving
The room decides who is in the call, not the tab. Closing the call's tab starts the reconnection window rather than ending your part, and opening the same address again puts you back where you were. Closing the chat's tab does not drop you out of the channel either, as long as the call is still open — you leave the channels when the last of your windows closes. Only Leave, which asks first, is final. The tab always shows a way back to the chat along its bottom edge: there is no conversation inside a call.
See also: Channel Conference · Sharing a Conference Link
