I saw a similar but even stranger situation DFW-TPA a couple weeks earlier. A man boarded with his wife and child, but his boarding pass from the kiosk was invalid. They let him all the way on the plane, there was someone in his seat, and they asked him to wait in the back. A few minutes later a FA came and asked him to speak with the GA to get everything straightened out. They shut the door after he deplaned and the flight left with his wife and child! Very strange, since there were still empty seats on the plane.

The wife and child didn't freak, so I guess he must have texted that he was out of luck.