Episode 20 of Season 2 is a dream of Nathan's if everything had happened in reverse. In this dream, Lucas goes out with Peyton and the love triangle between them and Brooke didn't happen. However, during the scene at 26:48 where Peyton is dumping Lucas, you can see the drawing she did in the reality world of her, Lucas and Peyton shooting a heart which symbolises their love triangle. This drawing shouldn't exist.