FRESNO, Calif. Truck driver dies after pinned while making a delivery

Reporter said this truckers partner didn't know why he was behind the trailer?
My first guess would be he was opening the trailer doors,it is clear to see in the video.
The trailer had barn doors,he was probably swinging the doors open.

If he had a full load that was unsecured at the tail he would have wanted to be as close to the dock as he could & still be able to swing the doors open.
However if he was not worried about anything falling out the back he'd have been better off to open the doors on the flat surface at the top of the ramp.

These issues are things I had to deal with over the years,however in each case,I always made sure I pulled both brake buttons before getting out,of my tractor.
Sad to think this trucker may have forgot to set the brakes?