"Supermarket" doesn't mean large chain store, it just means large store containing both food and household items. Plenty of locales have local supermarkets, either as singular stores or small regional chains. Whole Foods started this way. It was six years after the first store that they first expanded outside Austin, and their growth was fueled by buying lots of these small chains.[1]
I would say it's not only possible, but likely that some of these chains used a pro/con mask stance to distinguish themselves in certain regions of the U.S.
Everywhere I go had a mask policy posted but that doesn't mean it's actually enforced. If I had a dollar for every person I saw "wearing" a mask that wasn't actually covering their mouth and nose, I'd have retired last year
I would say it's not only possible, but likely that some of these chains used a pro/con mask stance to distinguish themselves in certain regions of the U.S.
1: https://en.wikipedia.org/wiki/Whole_Foods_Market#History