Based on my experiences working at another store in the same retail vein (a slightly "classier" store with color scheme that would suit the GOP), he might have a point in the broadest sense. I got hired about a week before an acquaintance of mine from high school, both of us as cart pushers. Three years later, he's a front end supervisor at a different store and I still push carts for just over minimum wage. He worked hard to get where he is - worked as many hours as he could, got as much training in different areas as he could, and he was qualified to be a supervisor within about a year. However, his only commitment beyond work was community college. To my knowledge, he didn't even have a girlfriend at the time. So yeah, he was capable of putting in a level of work that someone who had kids who lived in a home that they themselves had to pay for probably wouldn't be able to.
That said, that ain't Walmart, but since Walmart has 8,970 stores I'm inclined to believe that at least tens of them work like this guy says, if not hundreds.