if the colts did NOT snap the ball, they would have not run a play, they may have gotten a penalty for delay of game, but if they didn't snap it, there would have been no illegal formation play. with no play being run, NE would have HAD to take the delay of game penalty moving INDY back 5 yards and replaying 4th down. Because the ball was snapped the illegal formation penalty could have and was declined, turning the ball over on downs.
I THINK the whole point of the argument was the center was NOT supposed to snap the ball, had the center done what he was supposed to do, INDY would have been 5 yards back replaying the down.