When you're in a mob, you don't have a lot of choices- its either keep moving or fall victim to a trampling yourself. Walmart is the cause of their employee's death; surely his family has already received a massive settlement to make the matter go away. Since there is no union at walmart, there is no one to argue in defense of employee safety here. This will be summed up to people being inhumane, oh and by the way it happened at a walmart (but could have been anywhere).
For a price, this mob could have been well contained and controlled, but profit is paramount to Walmart.
If you're going to whip up a frenzy, you'd better have proper barriers in place, employees trained on mob mentality safety issues and heavy, heavy security. Rock concerts do this, so do political rallies, why is walmart allowed to let an unsupervised mob form in their parking lot?
Walmart is just as responsible as the night club owners who cause death by having improper emergency exits, or the miscreant that encourages the start of a riot.