[unfortunateface]

Facebook App copies your phone book.

Facebook App copies your matches phone book.

Facebook finds that your phone book contains your matches number and vice-versa.

Facebook suggests your match as a friend and vice-versa.

Nice and simple.

[r3bl]

Exactly. This article basically just talks about how you gave the permission to an app to use your address book and then complains that it's using your address book to identify who you should add as a friend. It's your fault for agreeing to install an app that requests these permissions without understanding why it needs those privileges from your smartphone.