As I understand it: 1) Another friend had your name and your phone number or email address in a contact list. 2) Facebook got access to that contact list. 3)

As I understand it: 1) Another friend had your name and your phone number or email address in a contact list. 2) Facebook got access to that contact list. 3) Facebook matched your entry in your friend's contact list to your Facebook account. 4) Facebook added any new numbers or email addresses of yours that your friend had (but that Facebook didn't) to your profile, but not anywhere you could ever see them. I imagine two major sources of this contact data are 1) Facebook phone apps that access user contact lists, and 2) the functionality in which you give Facebook your email address and email password and Facebook logs in and scours your email for the addresses of your contacts.