...some tourists don't know what's good for them. This should teach a lesson, don't act stupid or arrogant so you won't get beat up.
I've watched an uncut video carefully and this is what happened: The son of the British couple looks to be drunk, he rudely bumped into the Thai guy and shoved the Thai guy first. Then the Thai guy retaliated by pushing him from behind causing him to fall and hit his head on the ground. Then his mommy and daddy both turn around started confronting the Thai guy. His mommy eventually slaps the Thai guy across the face. His father was also nagging and causing an altercation with some other Thai guy as well. As they all decided to walked away, that's when this other Thai guy started punching them. He punched the Daddy first, knocking him down, then he punched the Mommy knocking her down too. The kicking to their faces and head continued knocking them all out cold.
What the tourists should have done was not retaliated and just walk away for their safety and happy travel. Or they should have called the police instead, if they insisted on confronting the Thai guy.
The Thai guys went over board with their actions, no excuse for beating up senior citizen folks in such ways.
Moral to the story, they all had it coming to them.