Not exactly, FEC basically means you add in redundant data to your transmission so that if some of the data is lost, you can “rebuild” the missing data from the packets that did arrive. The cost of this is extra bandwidth spent on the redundancy, as well as a little latency.
Rollback is as you say, if the game loses connection with your opponent, rollback 1) uses your opponent’s past actions to predict what they will do next and then presents that to you as if they did it then 2) when the connection is restored, reconcile (if necessary) the difference between what your opponent actually did with what it predicted, rolling back if needed.
