Walmart isn’t a supermarket, it’s a hypermarket, which isn’t really the same thing. This isn’t specifically a US distinction: it would also not be called a “supermarché” in France for example.
Most of them do have a (relatively small) grocery section, but are primarily dedicated to non-consumables like clothes, children’s toys, furniture, electronics, etc.
Whereas a typical supermarket (e.g. Safeway, Fry’s, Albertsons, Whole Foods etc.) might have a relatively small section of all of the above, but are primarily dedicated to food.
Exactly. His talking point seems to be, "In America you can go to a Tesco and buy a gun!" which is not remotely true. Replace with whatever stores you like in Europe (Carrefour, Aldi, whatever).
Never mentioned Tesco, never mentioned grocery stores. That's just you putting words in my mouth.
“Grocery store” and “supermarket” mean the same thing in most contexts in colloquial American English. What distinction are you drawing between them?