I somewhat suspect that this item is a a twist on something that may have actually happened. The potato is in the nightshade family, and Europeans initially suspected that it was poisonous. I would not be surprised if certain members of the clergy, often the most educated people in the community, had warned people not to eat potatoes. If this was true, the common person may have not realized that the fear was that they were potentially poisonous, instead just assuming that they were evil.
Keep in mind that this is pure speculation on my part, the only things above that I know for sure is that the potato is in the nightshade family, and that some Europeans thought they might be poisonous. The rest is mere conjecture based on this information.
