I think it's entirely possible that the guy in the video might have taped it because the snake was doing something "weird." Cutting the head off and seeing a snake still moving although it may be known to us that they do this, he may have saw that and grabbed the camera...
Again, not everyone knows the "proper" way to kill an animal. I would bet if you walked down the street and asked people what they think the most humane way would be to kill an animal (other than euthanasia) they would say to cut off the head.
The video is quite sad and it's very uncool to laugh about an animals suffering but I know that when I was a kid growing up on a farm, my brothers would kill poisonous snakes and other wild animals too (if they posed a threat) just to keep us kids safe. Out there, it was just a part of life and nobody was ever called in to deal with an animal. It was never an easy or fun event and we were taught that taking a life should never be fun, be quick and as painless as possible and always have a reason. Respect the animals and if you can, just avoid them but not everyone is brought up that way. "Snakes are scary" although we may not see it that way, is often the norm. In this case, one of my brothers probably would have killed that snake too as it was in a wood pile and we had a lot of bonfires where people would have come into contact with that woodpile quite often.