I generally agree with your skepticism, although the original source is the WSJ and I generally credit them with an elevated level of economic literacy.

Rationalizing your question: Amazon and Walmart predominantly sell shrink-wrap manufactured items with nearly unlimited shelf life and minimal variability. The supply chain is very different and much more forgiving.

Walmart does sell groceries, but it's unclear if they're especially successful at it, or if their prices are especially good. I don't feel there's enough information here to encourage or discourage your skepticism.