My shooting really is not very good, and I think that it has to do with my eye dominance so I would have to change my eye dominance with some training.. and surely you are referring to a long rifle with a accurately adjusted scope and surely with either a tripod or some kind of a surface to rest it on (not holding the rifle.. since that would be even more difficult). Surely.. scopes get thrown off frequently, and so there are needs to do target practice to make sure that the scope is accurate.. .
Sure, maybe it is true that a lot of folks can train themselves to cause 200-yards to be an easy shot.. and yeah of course that is around 2 football fields.
Another thing is that I would imagine if someone is shooting to kill then they would be shooting for a headshot, so the fact that the shot hit the neck may well mean that he missed, but he missed in a direction that ended up being quite effective.
I doubt 200-Yards is easy... even if you think so. Maybe others agree with you, and that is o.k, and your proclaiming to be able to make that shot with 500 yards? Have you consistently hit targets (like target practice) at that range? 500 yards is holy shit.. half a kilometer. I have my doubts. Call me an arm chaired skeptic.
LOL, I could make it offhand with a carbine 500 yards with open sites.
I am a Marine, we don't fuck around, I also has 20/10 vision most of life until recently which doesn't hurt.

I don't think you have had any training if you think 200 yards is far, especially with a scope in the prone.
FYI
minimum range on a marine rifle range is 300 yards.BTW, Professionals do not do headshots its not conductive to a kill as anything can happen to make a head move. Torso is the kill shot if your targeting humans, head shots are for people that don't have a clue and yes he got lucky and caught the neck whether he was shooting for head is debatable as he was probably going for torso but did not adjust his elevation for how close he was and shooting downhill. He probably had it zero'd for 300 yards. What you need to understand it the guy was a sitting duck, a target not moving and the kid was prone (lying down) with a long rifle and a large caliber round. It was was is termed a turkey shoot or fish in a barrel.
BTW, I didn't see where they said he had a scope but haven't read anything on it except a small paragraph to see if he used a carbine or not, you got a good link for all the specifics?
I don't know much of anything more specific (in any material way) beyond what was posted in this thread, and I think that I got the 200-yards from this thread.