Wether or not they invented it, the Belgians stereotypically eat more of those than we do.
Also potato in French is pomme de terre (ground apple) so French fries are often called pommes frites i.e. fried apples. In Astérix It is basically stated that they are frying slices of regular apples since they don’t have potatoes yet, much like the britons are drinking hot water with milk since they have no tea yet.