It sure looked like Roethlisberger's arm was moving forward when the ball came out. But the officials allowed the play to continue, and Giants' Michael Boley picked it off the ground and returned it 70 yards for a score. The play should have been ruled an incomplete pass, but the officials didn't overturn it after a replay review, which put the Giants ahead 14-7. Apparently the tuck rule only applies to Tom Brady.
Even if it was a fumble, it certainly wasn't a touchdown. Steelers tight end Heath Miller was pushed from behind as he closed in on Boley, and the officials should've called a penalty, which would've kept the turnover from being a touchdown.
This is one of several questionable calls that have gone against the Steelers in this game.