The thread is laughable. You think MS lawyers are so inept that they would write an agreement that would have a loophole so that a non developed Bungie game could be ported by Bungie for other platforms.
People also need to realize MS did not let Bungie go 100% free anyway. MS certainly still retains some ownership as well as a right of first refusal for Bungie developed games for some time frame.
Its libraries that sell systems not a single game.