There is no difference to being up 12 vs being up 13 when Florida is going to get two possessions the rest of the game. Even if you miss the 2-point conversion (up 12, or down 2 if Florida scores 2 TDs), a FG still wins you the game same as it would if you had kicked the PAT (up 13, or down 1 if Florida scores 2 TDs)
You lose nothing by going for 2. If they made the 2-point conversion, the game would've gone to OT. Butch made the wrong call.