"but have no idea how Linkedin associated you with them."
I'd hope most people round here can work that out, as it is largely by tracking multiple common contacts. If you know Joe, Steve, Helen, and those three all know Kevin, it isn't a bad guess that you might know Kevin.
Facebook recently suggested I knew somebody I used to work with about 20 years ago and I have absolutely no idea how they found the link. I was posted to work on a client's site for a few months and I was the only one from my company who was there and so knew this person. As far as I know therefore we have no other acquantances of any kind in common, I don't have their phone number or email address in my phonebook, and I've changed my contact details since I knew them!
The only thing I can think of is that maybe they searched for me by name within Facebook, but it's certainly more than a bit spooky that Facebook thinks there's a connection!