OKline,
I interpret the video the same way that you do.
You can see that the train is lined into the hole and the diverging signal is apparent as he approaches ths siding.
If you watch the video closely, you can see the entering signal into the siding go red in his face as the oncoming train (illegally) occupies the OS. The crewman bailing off the side of the oncoming unit should be a good indication that somebody woke up just a bit too late to do any good.
I interpret his setting the air to make sure that he is going the prescribed speed through the turnout and to make sure that he is going slow enough to stop when he reaches the other end of the siding. Just an additional reduction to control his speed. If he would have big holed, the air would have blown loudly and then the blow would have stopped. You would not have heard the additional slow set and the bailing off of the independents.
If I were conducting the investigation (which I wouldn't because I'm not an official), I would have congratulated the crew of the train going on the diverging route for keeping their heads in a very stressful situation and not panicing. Of course the crew of the oncoming train, if they had both had their rest, would have been down the road kicking rocks.
Rick