You're right. It's certainly bumpy. Was it filmed with a video camera, or camera phone?
10 yo Sony video camera. The ride compared to loco hauled stock, is very marked. I'm right over the bogie and it picks up every rail joint. We've got so used to welded rail. However I think that this is the best way to ride the line and the closest to the ride you'd have got in the Shefflex/Ford railbuses.