Even if you've never used Facebook, you have a "shadow" account, it is a well known fact. Every time somebody you know upload their contacts into FB, they link them with your shadow account, or create it if not already there, as a strong possible match.

I have started to use Facebook recently as I needed an account for work so decided to explore a bit, my biggest problem with Facebook is that your "feed" is made up of things that your "friends" liked or posted etc... but in what seems a random order, and not all of them appear. One has to wonder what kind of weighting they apply to each post to decide if it will make it to your feed or not.

Twitter has brought something similar recently, but at least you can disable it and get a sane timeline - Just tweeted about this today (check my profile for account).