My impression is it may be a guy who had had a bad day and getting the rear wheels trapped was just one thing too many.
I saw a guy once who finally got into the dock at a difficult location then it was a struggle to get out, he had had enough and just drove over the curb and across the lawn, through the decorative bushes and just kept going.
I couldn't be a truck driver, In my hot headed youth I would probably have lost my cool at some point and done something regrettable like this