I think your definition of scam is a bit off...because every app in the app store would be qualified as a "scam".
Anyway as I can see that you failed to read for comprehension I must reiterate that allowing next-door to read your Facebook profile in no way authenticates you to the site, nor does it provide them with your profile picture.
If you're the first person to login, the site will get an empty list. Only the set of your friends who have previously used the service, will show up if the service queries fb for your friends.
That was confusing and I considered stopping. I went through with it anyway, but that part was strange. Why do you do that?