Sorry, I don't see anything rude about it. If the assistant didn't have to climb on the roof to protect the trailer, he would have been right there with his own rig. Why should he be at the end of the line just because he had to compensate for the short comings of the campground maintainance crew? Your frustration should be directed at the campground, not it's paying guest, who had to take extraordenary effort to protect his property.
EDIT There are two ways to avoid the dump line. One costs more, and one costs less. You can spend an extra $10 and find a campsite with full hook-ups, or you can boondock it and find an empty dump station on the way home.