You're writing from the narrator's perspective. Think about: If you're telling a story about your friend, you still know more about yourself than you do about your friend. So when the narrator meets the main character, it's okay to have the narrator's thoughts and backstory, but when you edit you can go back and control just how much of the narrator you want to show versus how much of the main character. It's another balancing act in the writing game.
It's good to know things about your characters, even if it never makes it into the pages of your book.
- Off the top of my head, I'm thinking about _Great Gatsby_ where Nick is the narrator, but Gatsby's still the main character. It works, because Nick is still a character - emotionally and physically attached to the other characters and the outcome of the story.