I unfroze this chat room and then noticed the following in the rooms list:
The timestamp (8m ago) is when I unfroze the room (generating a message from Stack Exchange in the room), but the attribution is wrong. Isaac has the last user message in the room, but it was more than two weeks ago, not today. But the layout of the information suggests that, 8 minutes ago, Isaac posted something in the room.
I don't think the timestamp and last-user record are supposed to be independent, because I've seen rooms that go days without user activity but have active feeds and that activity doesn't change the time. This seems to be specific to unfreezing (and perhaps undeleting; I didn't test that).
The current behavior seems like a bug -- I expected it to either say "14d ago Isaac" or "8m ago Stack Exchange", but not one from Column A and one from Column B.