Point of order - only you Yanks call them 'French Fries' in Europe we call them 'chips' or 'frites' (short for Pommes Frite) en francais.
To suggest that it took the French to combine hot oil and potatoes is ludicrous (who brought the potato to Europe anyway??). They may have introduced
them to America (and that's debatable) but the concept developed simultaneously across Europe
Mayo on chips is popular throughout Belgium & Holland and not uncommon in the UK
Not being funny but @ the OP - did you travel to experience different cultures & try new things or just to confirm that 'abroad' is different?
Were you as outraged that McDonalds served beer or that people actually spoke Dutch?
I think this was started in Belgium; that's how the Belgians eat their fries. It sounds disgusting, and incredibly fattening, but I haven't
actually tried it.