Now, millers were indeed a stock medieval target. They cheated their customers of flour. They overcharged the lord's serfs who were compelled to come to them. They were rich and the lord's favorite.
But what this story had was a miller who could stop down the village by refusing to grind the grain.
In point of fact, when serfs had too much trouble with uppity lords, they would resort to hand querns and grind their own. Yeah, slow and difficult, and hard on the person doing the grinding. But you wouldn't starve. Especially since in this story there were no laws compelling them to use the mill, so they did not face legal penalties for doing it themselves.
Shortly after adopting a new technology, especially when you are doing it for ease and not for doing something new, you can revert back to the old ways a lot easier than it may look.