If you or the other person has the facebook app on your mobile phone, facebook downloaded your contacts from your phone. Facebook then recommends friending people in your contacts who have facebook accounts.
That's just it. We've had two face to face meetings, and some landline phone conversations -- maybe half a dozen emails on my work computer. That's the extent of our "relationship". No contacts. Never called him from a cellphone. Nothing. Don't know how Facebook can make a personal connection from that, but the fact that they can freaks me out.
Unless they got the information from HIS cell and crossreferenced me.