I think that works based on location. A few years ago there were reports of people who shared a psychiatrist being recommended to each other, based on their frequent visits to the office.
If she searched for you, it can make you show up in the recommended friends list
What about friends who are two degrees of separation? I suspect your social graphs are closer than you might realize.
I've had this with someone who I emailed (completely separate from Facebook) being recommended to me. The only logical conclusion I could come to is that Facebook was mining their emails for contacts.