I guess he is asking if a healthy person can die a natural death. For natural death, usually there is some scientific reason, but I have seen a Grey's Anatomy episode where a person survived many surgeries but couldn't survive a small very regular procedure, and her autopsy was also found clueless.
Again, that doesn't mean there is no scientific reason. It just mean the cause can not be diagnosed.
if i were a muslim at the mo i would have merely said" subhanallah" to justify my lack of understanding, its just not that simple anymore!
I also understand the complexity of the human body, but seeing science use the term "natural death" for something (an illness) it couldnt diagnose (prove), kinda makes me think of "religion" used to claim "gods" with no proof!
so since science has not yet reached the level required to provide flawless diagnosis of a humans health, we will have to consider the term "perfectly healthy" being nothing more than "good, with room for things to go wrong"