You claimed the truck was filthy, and stated you refuse to drive it.
You return to the office, and the boss comes out, which I assume he thought you were over reacting, then he fully agrees with you.
I can’t see what you did wrong, your boss backed you and was rightly annoyed that an expensive vehicle was trashed, by a driver who is obviously an idiot,
You did the right thing, don’t worry about the other driver, he has no respect for you or company property.
If I were given a new truck it would be kept ■■■■ and span . . Why, because it would be my home… even if I was a day driver with a truck I would keep it ■■■■ and span, for personal price and self respect.
You did the right thing.