I unfortunately can't get behind the paywall - does the article mention or does anyone know how much of this actually has to do with the stockpile.

I would assume stockpiline would ultimately be a smaller factor compared to the issues of business shutdowns. I'd imagine, though I'd love to see data, that most of this just comes from an increase in online retail overall (with Wal-mart being just one of a few companies equipped to handle this) and the lack of money being spent at restaurants for everyday meals (Wal-mart is America's largest grocery store)