[sdiepend]

Have you used it on mobile and shared your contacts? Might they have had access to your location(GPS or maybe to which wifi you're connected).

Interesting article: http://fusion.net/story/339018/facebook-psychiatrist-privacy...

[funkyy]

Or they just suggest people based on common locations that you and they visit and where they spend their time.

[spraak]

The mobile app's contacts seems very likely. I didn't realize it would spy on those, but not surprising.