Yellow jacket diets change over the season but I'd bet that turned-over bucket they incorporated into their nest was full of some kind of food source (looks like the kind of bucket I saw corn syrup sold in once).
Also, these look a lot bigger than typical jackets, though they clearly aren't bald hornets. I wonder if they were crossed, Killer-Bee style (Africanized Honeybees). The nest doesn't seem to be from either of the two US species. It is more of a hybrid between the subterranean/hollow structure jackets or aerial Hornet-style jacket nests except MUCH bigger. I forget which, but one is invasive.
Perhaps this dead guy was a Dr. Moreau type who tried to make a hybrid with a large aerial Hornet species with this not-quite-disastrous (yet?) effect.