Industrial accidents happen in the US too, although I don't know what rate vs China. I think the fact that their factories have surveillance at all shows they are taking action to improve safety. You've got to consider, the population is 1.4bn, so there is going to be more freak accidents caught on camera.
they are extremely good at suppressing such videos internally
they will sometimes allow something like the particular video you mention (I was living in China when that video went viral, this was about 10 years ago) because it directs anger at individuals' bad behavior, not at the government (in fact, in favors the government making and enforcing rules to disallow bad citizen behavior)