In the wilder palces in central and south America, the cheap shotgun is the tool of choice for both hunting and 'other' things. They are the staple of trading posts and every village has at least a few of them.
I can only wonder at how some of the poor locals see the foreign adventure tourist traveling through their territory. He just may seem like the Santa with a sleigh full of goodies, except that he's not going to give themup easy, so it's easy to just shoot him and steal everything he has.
This is the problem with a lot of these young adventurers, they don't realize that they ain't in Kansas anymore, or Pee wee's playhouse. Forget your miracle micro fiber clothing, and high tech goodies. It may be better for your life span to look like a local from a distance in faded and frayed cotton, in a old canoe instead of a high tech Klepper or Folboat.
I know that when Karen and I did the rainforest trip in Costa Rica, they told us to leave all our valuables in the hotel safe, and not take any flashy or expensive stuff with us.
There's no guarantees in life, but traveling to a basicly lawless place, it may pay to look a little more like a local. These guys just may have scoped him out, and sized him up before the attack, and had decided he was worth killing and robbing.