A very speculative point not based on reality, really thin ice for this argument sicne we could come up with countless scenarios of what may or may not have happened. I'm trying to focus on what actually has happened.
It wasn't a study but an interesting note made by the authors of the book, to find details on the RA-5C crewman's adventure is actually pretty hard and the second account I've only seen in that book and even in there it is only an anecdote with no details or name fo the aircrew.
'Everyone' didn't expect they would be taken alive in Vietnam, there were several well-known instances where contact was established with downed aircrew then shortly thereafter lost due to locals or enemy troops killing them after being discovered. That is actually a source of controversy for several aircrew who were originally assumed to be captured based on the contact established after being shot down but later declared KIA. There were several similar instances in WWII and Korea as well, especially when locals were the first to encounter downed aircrew.
His was an escape, a completely different scenario than the one we are talking about, unless you can somehow smuggle that M4 into a prison camp.
Yes, training.