Let's go to the holy grail of hitches and gander at their thoughts on causes of sway, compare them to the video and the account from the owner of the rig. Then eliminate the ones that don't count. I don't believe the driver was an idiot or a maniac. Causes of other than trailer induced sway will correct themselves when the cause ceases. This kept getting worse instead of better as the accident unfolded.
https://www.propridehitch.com/what-is-trailer-sway/This one was obviously caused by an irregularity in the road as he drifted out of his lane onto the margin, his swerve to get back in his lane and, not being trailer induced. The sway was pretty bad. It corrected on it's own with the driver keeping the TV in line.
https://www.youtube.com/watch?v=ABg20TEfY-8
