I really don’t get what their end goal was here, other than to beat the shit out of someone.

probably just this, taking out their frustrations on someone who was already marginalized. some people have no problem with punching down.

NOW, if there was any kind of policy that led to this - such as punishing employees for losses, punishing the entire store, etc., sains should be held partially culpable. But most modern institutions would prefer to keep their employees away from fisticuffs.