There’s fault and then there’s responsibility. If the driver is acting as a Walmart employee, then he’s acting as their agent. Walmart is responsible for his actions.
True to a point, but we can really kick the anthill on this one. Suppose you need your living room painted and have reached the age and point of affluence that you no longer want to do it yourself. You hire a local painting company of good repute. On the way to your house, the van rolls through a stop sign and wipes out a class of preschoolers being escorted to the park. Are you liable for what "your employee" has done? The driver was, after all, only there in the first place because he was working for you, and on his way to your location.
You will answer that the driver was not your employee; he was an independent contractor. (Try this if you are a trucking company, and hire independent driver-operators .... This is a big issue.) You might get away with this if the guy is a one-day hire, but what if you are having your basement gutted and redone, and the crews are on site for a month? Or if your cleaning lady did the deed, and she has come in once a week for ten years. You clearly have a long term employment relationship with her, and hopefully have been reporting income and withholding taxes, or killing the preschoolers may be the least of your worries. How much of an employment relationship has to exist before you are liable for your agent's actions? And are you liable for their actions while they are in transit to and from your home, or only on-site?
The point is, the plaintiffs' bar is a green-seeking missile homing in at supersonic speeds on the deepest pocket. In this case, let's assume to driver was a company driver, fully in the employ of WalMart. It's still problematic: do you think employers should be responsible for what their employees do (or don't do) off the clock? How much diligence is due diligence. You had better hope that the guy you hire to paint your living room doesn't deal drugs on the side, or you might be rooming with Bubba some day.