I don't have a problem with the call.
There were 4-5 defenders right there and multiple guys had him grasped.
As far as forward progress goes, I'm not sure about all the intricacies of how they define it but I could see there being small inclusions of the rule where he wouldn't be making forward progress.
Had he been tackled just before breaking loose, they're spotting the ball a yard further up field than where the tackle would have occurred. After blowing the whistle, they tacked on a yard to spot the ball where they concluded the play ended in order to credit him for his forward progress.
1st and 10 at DAL 20 (Shotgun) T.Romo pass short left to D.Bryant to DAL 33 for 13 yards (S.Brown).
He advanced to the 33 before his initial progress was stopped by the Cleveland defender. From that point on he is in the grasp of the players until breaking free and he never gets back to his furthest point of advancement. He breaks loose at the 32 (or abouts) but during the time when he's in the grasp he never makes it beyond the 33.
Throw in the fact that they aren't going to let guys take unnecessary shots when they are stopped by 3-4 guys if that player isn't clearly pushing the pile while advancing the ball. Had he taken a hit that resulted in injury, the NFL would probably get crapped on by the media for letting a play go too long.
As I said, I don't know for sure how the rule is written or defined but I can see a line being drawn and combined with the safety emphasis I don't have a problem with the whistle.
A player who's advancing the line of scrimmage with each step versus a player who is regaining lost yardage towards his furthest point of advancement.
If you make it to a point and then get driven back 5 yards only to push the pile forward 2 yards, have you really made forward progress? Regardless of pushing the pile 1, 2, 3 or even 4 yards when the play is over the ball gets spotted at the point of furthest advancement which was still further up the field than the distance you could recover after getting driven back.
As I said, not entirely sure. It's likely I could be wrong but I can't look it up right now.