If the play would have happened under the two minute warning or was a fourth down play/try, then the fumbler is the only Team A member who would of been allowed to recover and advance ball. If another player on team A would of recovered the ball, it would revert back to the spot of the fumble or the recovery spot, whichever is worse. As the play occurred outside the two minute warning and was not on fourth down/a try, then a recovery by the Steelers would of resulted in a touchdown.
The rule about fumbling forward says that if the ball is fumbled forward and out of fumbles, it reverts back to the spot of the fumble.
Also, aside from the officials erroneously saying the ball crossed the plane of the endzone, the play was handled correctly.
http://sports.espn.go.com/nfl/news/story?id=5726781