It doesn't make a whole lot of sense, but that seems to be the case.
I understand that purifying Sasuke of Orochimaru would, say, removed the cursed seal. Since the seal is a part of Orochimaru.
But causing him to just...forget all of Oro's techniques. That doesn't make a whole lot of sense. I mean, what does being able to Summon Snakes have to do with being controlled by Oro?