I've ridden in fresh chip-seal before, and I can attest that you get 'sprayed' with stones whenever a car goes by. It's not the car's (truck's) fault, it's more like splashing through a puddle that goes on for miles.
The policeman obviously didn't understand vehicular law: driving on the shoulder is illegal, even though it seems to be tolerated in the case of bicycles only because it makes things easier for motorists. I've found the best way to handle a dumb cop is to go along with him - until he's gone.