Yeah, boiling bodies for a long period of time is how they prepare/make medical demonstration skeletons. My guess is the clean up personnel and police waited to retrieve the body so the soft tissue is all boiled off and evaporated, then retrieve the skeleton and hand it over to the funeral home and family.
Very sad and nasty, but as it's already been said the guy was asking for it. They say not to venture off the paths at Yellowstone, and there's a reason for it. Between this and the people that kidnapped a buffalo calf and drove it around the park, it seems like there's always people doing stupid dangerous shit there. They're probably going to have to increase security to protect the tourists from themselves.