That's like saying "cake eaters are not a protected group" if a pastry store refuses to sell a cake based on, e.g, customer's race (a protected group). I get it that businesses can decide for themselves which types of IDs are acceptable (so de facto they can discriminate). But if there was a discrimination case here, it would be based on national origin, which, in turn, would be a violation of Title II (public accommodations) of the Civil Rights Act of 1964.