nevermind I was wrong! Basically, once you clicked on chapter 2 you'll get asked some questions and apparently in order to progress you have to say you didn't eat anything at the circus, which will (for some reason) allow you to continue with the story.
edit: yeah no I was right the first time. I mean, doing that does give you a new initial scene (I think? I haven't seen it before), but inevitably brings you back to the day you meet the Jester for the first time. Anyway, I'm pretty sure the "Chapter 2" button was added to the menu back when the game finished with Pierrot kidnapping you to the Freak Circus. People who downloaded the game in its first version probably needed the button to continue with the story, but we downloated it later on, with chapter 2 already implemented in the gameplay. Essentially, you (we) already played chapter 2!