Interesting that nobody in the whole wide world seems to know the NFL pass interference rules--and that the rules contradict themselves.
As the ball sailed at least 10 yards past him, a Colt receiver slowed to a stop, creating contact with the Steeler who was covering him. The officials ruled defensive pass interference. This was definitely wrong for one reason, because it was a case of "Contact that would normally be considered pass interference, but the pass is clearly uncatchable by the involved players."
But if we forget about that, it was also a case where two of three other clauses mandate offensive interference, even though one mandates defensive interference. The offensive player was guilty of "Contact by a player who is not playing the ball that restricts the opponent’s opportunity to make the catch" since he was absolutely not playing the ball, and restricted the defensive player from continuing to run towards the ball. He was also guilty of "Cutting off the path of an opponent by making contact with him, without playing the ball." It's true that the defensive player was guilty of "Playing through the back of an opponent in an attempt to make a play on the ball." So both players should have been called for interference and the down should have been replayed--if the ball wasn't unplayable, which it clearly was. You can make a reasonable case that the last clause makes an unwritten assumption that the player whose back is being played through must be trying to catch the ball himself, and if he isn't, that one or both of the first two clauses apply. If so, then the play is offensive interference only. In any case, even if the ball is considered catchable, the ruling should not be defensive interference only.
Anyway, after the officials wrongly ruled the play defensive interference and wrongly denied the Steelers' challenge, the announcers only mentioned the uncatchable ball part of the penalty to criticize the ruling. One even said, "It was clearly [offensive] pass interference."
Takeaways.
1. The officials suck
2. The commentators suck
2. The rules suck