Facebook has quite a lot of information that you didn't give them, especially things like location data off your phone if you have their app on your smartphone. They also know lots more about you from your network of friends.

One of the clues to how much data Facebook tries to quietly take from you is their ad campaign to get users to enable their app to access various aspects of their iPhones as Apple as made changes in iOS to require explicit access authorization for applications to things like location, microphone, speaker, etc.