That holding call came at the beginning of the 4th quarter with Dallas down by 7 and Barber's 4th down conversion would have been the third 1st down on that drive. I think Romo felt like they were driving towards a TD there and instead they had to punt and 4 plays later Stallworth scored the 69-yard TD. I don't really see it as Romo throwing his line under the bus as much as saying that the play in question was a serious turning point in momentum and he would've liked to see what the team could have done with 1st down inside NE territory down by 7 in the 4th quarter.
Yes, I don't think he was accusing the holder but wondering how the game might have gone had that play been successful. I got the impression that he was talking about how competitive they were. TO was more diplomatic in saying, more generally, that they killed themselves with penalties.