Well, I'm not a doctor or medical professional of any sort so I honestly don't know. I was just presenting things that could lead to an apparently healthy young-ish man suddenly dropping dead for no apparent reason.

I didn't pick them totally randomly, though. I had a rationale: He seemed emaciated, which suggests something left him immobile for an extended period since he had food at hand. This made me think of strokes and snake/spider bites. The former could leave you permanently immobile, but alive. Without assistance he'd have died within a few days. The latter, depending on the sort, could leave you immobile and in great pain for a day or so, with a chance to recover and survive. But if he'd already become sufficiently dehydrated he may not have had the energy or wherewithal to care for himself.

There are other conditions which could lead to a similar outcome. Heat exhaustion, for instance, may not kill outright. But could leave you in a state where you need assistance and can't recover on your own.

Whether they'd show up on an autopsy, I don't know. But also per the article it was a while before he was found. So given a sufficient level of decay, it's possible these conditions wouldn't show up or would be sufficiently hard to detect (remember, the sheriff's didn't even want to pay $5k for the DNA testing, he wasn't a crime victim so their budget wasn't paying for a lot of analysis).

Bothrops or Vipers distroy blood or tissues. Would made unmistakable swelling or extensive inner bleeding.

Micrurus bites could be not so easy to detect but would not explain the weight loss.

And liver and kidneys were clean