The guy is a dick, common courtesy on most gravel roads down here in Montana would be to pull over, the faster car, truck, bike passes and takes it easy for a bit to not raise to much dust, then go as fast as you like. If you grew up around gravel roads, you got held up by stock trailers and grain trucks, and they always pulled over. The drivers knew the next day it might be them. But the world is changing, to many inconsiderate assholes out there. Forty years ago they might have got the crap kicked out of them at the next watering hole, today there just to many of them to bother.
motorcycles are like fly rods, you need way more than one.