Kain makes no effort to conceal his confusion. "Have I truly forgotten what?" Was there something that he ought to remember? If he did, he didn't recall. Goodness knows he'd have welcomed forgetting some of his time in the tower, or all of his time upon his dead world. His jaw sets. Let's apply some logic to this matter.

"If the both of us were in whatever place you last occupied, I am not the Kain that you knew. The tower held many souls, but yours was not counted among them."