Though it would have been nice if the marshaller had used and taught the signals correctly.
Care to elaborate? Looked pretty good to me!
As for "do they really think pilots can't follow a yellow line?" ...based on my observations of some pilot's parking abilities over the years, my answer would be no! Granted, this doesn't apply to all pilots, but some of the positions I've seen aircraft end up in when they've self-parked makes me wonder if they've spotted the yellow line at all. And aircraft aren't always marshalled just because the parking systems have failed, sometimes it's to avoid obstructions and hazards, and if you choose not to follow the marshaller "to the inch" then watch them leave you to it as you plough your aircraft into an obstruction.