I wouldn’t be surprised if those prions even all die in fire, they are otherwise indestructable.

Prions are mis-folded proteins.

All proteins will be denatured at high enough temperatures. When a protein is ‘denatured’ it just means that it breaks apart into its fundamental building blocks – into amino acids or just into much smaller chunks of protein. And a protein can’t be mis-folded if it isn’t folded at all anymore.

As long as you get the temperature high enough, all prions will be completely destroyed and rendered safe. Hell, if you get the temperature high enough, you’ll even separate the amino acid molecules into their component atoms, especially tearing the carbon atoms out of them to create carbon dioxide as the ‘fuel’ oxidizes.

If the people disposing of those bodies knew what they were dealing with, I’m sure they took great care to ensure the temperatures were plenty high. I wouldn’t worry about it. Prions are scary because they’re not ‘alive’, even in the sense viruses are. They’re smaller and more resilient than any virus and have no metabolism to feed, so they can theoretically last indefinitely. But high temperatures are an effective way to permanently destroy them.