That's the wrong metric. It should be obvious that the US market share of walmart on groceries, merchandise, and health don't conveniently sum to 100%, and that's not how you would present that data. You're looking at the % of WalMart's sales, not market share.

The answer is more like 25%: https://www.axios.com/2023/04/20/most-popular-grocery-stores

This is saying 58% of Walmart's sales are groceries. Not 58% of grocery sales are through Walmart.