That's not uncommon at all. It happens when someone assigned a FC seat no shows. The seat goes to the next person on the list. Sometimes the FA will walk up to the person and tell them a seat became available in FC and sometimes they'll make an announcement asking that so and so ring their call button and then they'll walk up and tell them. Happened to the spouse of a friend of mine the other day. Her husband, a Plat, was upgrading her.