I just read the story on ESPN.com. The man who died was only 35. This suggests that either he wasn’t in shape for a long run in the heat, or that he had undiagnosed heart disease already. Sometimes middle-aged guys just drop, after even moderate exercise.
I remember back in the ‘70’s some guy named Fixx started a jogging craze. He died while he was jogging, from a “silent” heart attack. He was 39.