The Walmart - DEF story sounds like they typical Walmart internet stories that constantly circulate. Like Walmart only sells defective ammunition that doesn't meet specifications which is why they can sell it so cheap. Guns at Walmart are cheaper because Walmart buys guns that fail specs. Walmart paint is cheaper because it's mixed with water so it's thinner and diluted. Food at Walmart groceries is food the major chains throw out.
These and a lot more always make the rounds yet no one has ever come up with an actual report to confirm it. It's always "I heard..." or "My neighbor knows a guy who had it happen to him...."
But it must be true. It was on the internet.
Just proves that common sense isn't common. Some people will believe any story. P T Barnum was right.