> That's kind of scary that you can get that information just by (if I read this right) having the user ID of someone you "matched" with.

Not quite... the API returns the Tinder user ID of all your Facebook friends that use Tinder. You can see who uses it, when they last used it, what picture they use there, etc.

You can also "swipe right" or "swipe left" using the API on anyone you have the Tinder user ID of, even if Tinder never matched them with you.

So it's scary in a "creep on your friends" way not in a "creep on strangers" way.