This is correct. During the break, the offense has like 40 players on the field—that’s where there is room to get in a big circle and talk. It counts as a substitution for the defense because they can’t know which 11 will stay on. The refs are supposed to hold the snap like they would after a sub. They didn’t, and that is their mistake. Bama should have had time to sub.
But a player can’t run off and then back on. That’s on Bama, and was rightly flagged.
As for the whole flopping thing, that’s clearly a bad look. Even Bama fans are ashamed, and rightly so. I wonder if it should have been an unsportsmanlike flag under the rules as they are. I also wondered, watching in real time, if he flopped after the snap such that the play should have been allowed to continue.