Per the article:

Sorry, Facebook. If you thought creating Libra was a big deal, whatever Walmart >does in terms of virtual currency will be much, much bigger

What the writer forgets is Walmart isn't in competition with FB. The Libra coin will be earned by people on FB clicking viewing ad content. Coins earned will then be redeemable at retailers who sign onto the FB plan. If true and it's relates to the actions of FB Walmart may just be going to jump on the FB list of retailers. It would only seem logical that Walmart would develop their own coin so they can perform transactions with customers of FB.

Walmart is already using blockchain technology for it's produce providers as it enables them to within minutes instead of hours find the exact location and vendor of any potential contaminated product.