If I understand correctly, the trucker was set up to roll coal on other people, and only made an exception for this specific kid on a bike. It's not "unhinged" to stand up for others who have been targeted even while you were spared — it's just common decency.
But anyone who "rolls coal" doesn't have a truck set up to always do that. They'll have a switch on their console which makes it happen (or something digital). You don't need to try to not roll coal if you don't want to. Probably what happened is the person just drove a normal truck and knows that diesel fumes are stinky and tried to coast by the bikers so there would be the least amount of exhaust near them.
Is there some way of knowing a truck is set up to "roll coal"? If not, then this could just be the OP thinking poorly of someone just trying to drive carefully around a family. It would be jumping to a very pessimistic conclusion without evidence.