I didn't say anything about a life vest. It would seem reasonable to me that he might put one on if he had one---but there is no way of telling. Occam's Razor is a principle advanced by Isaac Newton to the effect of "make no assumptions beyond what is required." The point is that the evidence shows that "the diver" was one of the passengers who happened to have some swimming gear he could quickly slip into. There was no scuba. He exited the plane along with everyone else. No mystery why he was there---and no ulterior motive. As pointed out above, Fuddy died of heart failure following the prolonged exposure. No sinister plot.