RIP David. I hate being right about this one. The most obvious answer turned out to be the correct answer.
Generally speaking, it takes chronic use of meth to work one's way up to hallucinating. Thinking you're being chased or followed, abandoning your vehicle in a panic and running from those hallucinations, shedding one's coat along the way because you get super hot in that condition. I've known addicts who have done all these things. It was also drizzling rain that night, so real-feel got much lower than the simple air temp -- he was wet in a white t-shirt and jeans, running full speed from his hallucinations, exhausting himself, out in those fields for a long time, until he just couldn't run anymore.
With meth, it's rarely an overdose that kills the user ... it's the meth lifestyle that catches up with them. In fact, I've not personally known anyone to actually OD on meth, and I've known my fair share of meth users (snorters, mostly smokers, and sometimes shooter-uppers). David is a case in point. He was not a bad person, I'm sure he was a good person (most addicts I've known are good people), he loved his family, he worked hard, I'm 100% sure he tried to get off the stuff many times and just couldn't, he was caught up in something he had lost control over. He had an addiction. And it killed him.
You don't know people like you think you do.