Facebook visibility...?

[coolwhip]

Let's say we have 3 people on facebook: person A, person B, and person C. All 3 people have been using facebook for a few years...

Let's say person A and person B have been friends on facebook for two years. Person B then changes his relationship status to "in a relationship with 'person C' ". A and C have never been friends, and person C was never visible to person A prior (nor visible to person A on person B's friends list). After the relationship status change however, person C is now visible to person A (shows up on the search bar when searched). Person A also now sees person C on person B's friends list even though they have never seen person B add person C as a friend. How would this be possible?
abraXus: Who is person Y? In this scenario there is only person A, B, and C.