Meeting the original

But Jon didn't meet Biff there. He met Sarah first. He would have expected Sarah to get upset, wonder why there was someone exactly like her. But what he didn't expect was what had happened. Sarah took one look at him and said "Oh, no, it's the real Sarah!" Then he realized what happened. He wished that everyone would think he's the person he's acting like. Everyone meant everyone--including the person themself. So not only did Biff think he was the real Sarah, Sarah also thought he was the real Sarah. But if Sarah thought Jon was the real Sarah, who did Sarah think she herself was?