By "the address books," may I assume that you mean the address books people have created in their Facebook accounts, not the address books on their computers?
No, I meant the address books on their computers. Those are what "friend finder" uses to look for "people you may know" who have Facebook accounts.
Wow! So people actually give Facebook access to their entire lives, so to speak.
In that case, I'll never be able to even begin to guess how the connection to me was made.
Ces't la vie!
Thanks.