I would say (take with many grains of salt, something that at least in its non-Himalayan form can't be culturally appropriated) that the act of taking potatoes from South America to Europe isn't in itself appropriation. It's part of a whole conquistador-colonial nastiness, of course, but otherwise it's just "cool, new foodstuff." That word "discovery" puts the historians in the appropriation camp, but not necessarily the explorers themselves.

I tend to think of food-culture appropriation as having more to do with putting traditional foods (in particular, preparations of those foods) into a context where the dominant culture is "discovering" them and making them "better" and usually charging a hell of a lot more for them. Like making a version of papas a la Huancaina with expensive ingredients and serving it in your highly-reviewed restaurant and then talking down the original as unsophisticated. But the historical context makes it more interesting, indeed. Just I would to hate to cook only with the ingredients my ancestors used that grew in their continent of origin!

Michael Twitty is always good on appropriation and cultural sharing in the African-American context - and not overreactive, either, which I appreciate.