[randomsilence]

Do all participants have iPhones?

Apple could have an almost complete social graph. If Y Smith is the common acquaintance between you and your friend, then it would be the best second suggestion if you want to share something in that part of your social graph.

[MobileVet]

Yes, there is some potential there... though I am pretty sure the other parties had not swapped contact info yet as they were new and only just met.