My friend and I were testing Share Play - it works very well - but something weird happened. His PS4 - the one without the game (Alien Isolation) in the drive - started downloading a patch for it. Obviously, it can't patch a game that's not present.
I see there's been a post or two on this...has Sony said anything? Hopefully it's a mistake and will be fixed.
It links games to your profile by the looks of it, I started downloading a Fifa 15 patch. I'm guessing trophies will be disabled until you purchase the game as well (I earned one but it didn't show in my list)