I think that it was a stunt gone bad. Perhaps the father and son were part of a network supporting the dopes and the kid thought the video was going to end before the knife fell.
I think your assertion has merit because he seeemed so calm when he was giving his name, rank, etc. in the video. Even before I knew anything about his dad and his politics, I thought his [Nick's] demeanor was really odd for someone about to be beheaded. It just didn't compute.
I think so, too. The orange suit stands as a factor. This was to demonstrate what an Iraqi or Afghan prisoner looked like...The "murderers" changed scripts midway!!