My take on the video.
Irrespective of weather the mustering should or should not have been being conducted at that time or not, the accident could still have been avoided.
Obviously had the cattle not been there no accident no problem.
Likewise had the truck not been there no accident no problem.
Thirdly had there been signage there would have been less likelyhood of as the truckie would have been forwarned and believe it or not they give serious consideration to those warnings on the open road
It was not really dark, more dusk/twilight. Visibilty to the sides on the downhill run was natural light so it wasn't full dark. In QLD at least stock are to be off the road 1 hour before dusk in almost all cases.
An aircraft flying that low over a road is so unusual that I have never seen one in over 5 million klms. It would have been an immediate distraction and I believe the jakes and likely the service brakes came on within normal reaction time of him identifying what the aircraft was. I say the service brakes as well becuase Jakes alone would not have slowed him down that quickly.
The drivers reaction to move to the wrong side of the road which commenced before the braking was between when he sighted th A/C and when he identified what it was, he was trying to widen his angle of vision to the corner to see what it was blinking infront of and above him.
The clincher then and the largest contributer to the accident is the car on high beam. In my opinion he was to far away to have spotted the cattle, he had done one of two things,
A. He was driving on high beam when at dusk he would had far better vision on low beam. Or
B. He had seen the aircraft or dust and hit the highbeams to have a better look. The flashing we see is indicative of him hit bumps and the lights bouncing not of flashing high/low.
The high beam almost certainly blinded the driver before they blinded the camera.
The truckie had already reacted and applied almost maximum brake well before he ever saw the cattle thanks to good reactions, and no thanks to being blinded by oncoming traffic. Not only that but he never overreacted once he did spot them. A swerve in either direction on a sweeping corner under maximun brakes and going downhill would have meant an almost certain rollover or jacknife.
The second voice is almost certainly a twoup driver who was most likely asleep in the bunk because by his reaction he saw nothing. Almost all trucks that are running twoup through there would be loaded not empty.
I would give the truckie a job. I think he handled an almost impossible situation admirably.