I was going to make a similar point: How did Dean ACTUALLY know that it wasn't a corner? Player protests isn't a good enough reason for him to come to a definitive conclusion that he got it wrong. The only way he'd have known for certain is for the 4th official to have seen a replay and told Dean via his earpiece. Which raises the question whether that is actually allowed within the rules?
Either way, Dean gave a decision based on what he thought he'd seen. That's not 'wrong' per se.
To me, going down the "2 wrongs making a right" route is a slippery path...if even-ing things out is an accepted practice then the rules need changing to allow a referee to reverse a decision before play recommences. So, if Dean had received conclusive information that it was a goal kick then blow the whistle before the corner is taken and change the decision.