I don't wish to watch that video. But I do know from personal experience that laughing at even serious mishaps is a cultural response.
In Isaan once I was on the slope of one of those fish ponds they keep, and slipped and fell. I managed to break my fall and avoid falling into the water, but the Thais around all laughed. I was quite shocked and for a moment had a flash of real anger - fortunately at exactly the same time I remembered reading a passage in the Lonely Planet (yeah, it was a while back) that mentioned this and that we should not take offense. I didn't and managed a forced smile back even though I was quite shaken.
But I wasn't drowning.
This is why swimming should be a must do school subject.