If the exploit potentially allows downloading and running of unsigned code after release in the app store, how else could one prove that it is in fact a hole, other than by releasing it into the app store to confirm the behavior?
That said, this guy broke the legal agreement that we partly rely on for trusted computing in iOS. He can be thankful if he doesn't get sued, and he should have gone about it differently if not willing to face the minimal consequences of violating the legal agreement.