MJ & Earl - interesting viewpoint. I haven't had any issues by going to my insurance company, but do know I don't do it right away. I do as others do and work through the different angles of discussion with the customer. When there seems no path to resolution, then I go to the insurance. I've had to do this less than 5 times over the past 7yrs, so usually I'm able to resolve the situation myself. But when they are insistent, then out comes the claim hotline. The times they've contacted the insurance, a claims adjuster was sent out, luckily in the instances they sent out a former auto body repair person. He was able to explain to the customer how the equipment was unable to do such damage.
Anyway - just a suggestion. People want to blame us for a lot of things. I agree that there had to be some type of catalyst that caused/started the paint removal, such as an imperfection or rock chip. I don't see how straight pressure from the hose would have done that, unless you stood there for a long time, very close, and held it in one spot.