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).