Great phrase, no? A shortcut for those of us who love historical fiction and hate the errors that some authors can let into the story.
Example: the medieval lord and his fair lady sitting down in 1253 to a hearty dinner of good old English roast beef with a side of potatoes and gravy.
Gravy I might buy. But the potato, along with a dozen other vegetables and fruits, is a New World import that didn't exist in Europe in 1253.
Ditto the tomato. And corn (American sweet corn, a.k.a. maize). The historical English, if they refer to corn, mean any grain product, particularly wheat. So if you're reading about a 15th century "corn merchant", don't think you've encountered a moment of Potato Hatred -- think wheat merchant instead.
Why do authors do this? I can't speculate on every possible reason, but among them must be haste; laziness; ignorance; and/or bad editing that "corrected" a reference to a veg that was correct for olden times to one more easily recognized by a modern readership.
But I feel as though Potato Hatred can cover almost any anachronism in fiction. My criterion: if it yanks you out of the book, has you scratching your head and thinking, "Whaaa--?" it's a candidate for Potato Hatred.