As for "what they mean by Region in English"...Americans would have no idea what they mean either. Our country doesn't really have much in the way of "geographical" boundaries for the production of certain products...it's fine to label and sell a "Wisconsin Sharp Cheddar (made in Texas)". Or a "Bourbon Whiskey" made in Colorado. Words on labels are generally pretty meaningless here.
But generally Americans who buy higher-end European foodstuffs expect Europe to have strict controls on what's allowed to be called what on a label exported from the EU. For example, although quite a few American sparkling wines can still be labeled "Champagne"[0], generally we'd expect that anything imported from the EU that is labeled "Champagne" would come from the appropriate regions as expected by the laws in Europe. Similar story with various cheeses that are typically stamped with D.O.P. / A.O.P. / P.D.O. -- if an Idiazábal is imported from the EU, I know it's from Basque/Navarre and produced according to traditional methods. If it's American-made Idiazábal ... I have no fucking clue how it was made or if it will taste anything like a real Idiazábal: Maybe it will be perfect, or maybe it will be completely wrong.
So in this case, as an American browsing high-end groceries, I figured "Dijon Moutarde" would be an "appellation d'origine contrôlée" but I am mildly surprised to find out that it is not, and that I should look for "Moutarde de Bourgogne" instead.
Thank you.
0: https://blogs.loc.gov/law/2016/07/the-protection-of-champagn...