Don't know about China specifically, but "working ridiculously hard" is just "working" if everyone around is doing the same and you had no points of comparison.
If you've seen enough people graduating into non-working class, or you have had yourself, that changes your perspective.
I guess that would add credence to the culture element. All of east Asian shares in this practice really. Given a structure/framework in which to work productively, they tend to really crush it economically. However it seems this often comes at the expense of other aspects of society (underemployment, low fertility rates, elder poverty, deflation etc).
Looking broader at South East Asia, the Chinese minorities in countries around the region are know for working hard and being successful, often more so than other locals.
I'm inclined to think about it in terms of east Asians than strictly ethnically Chinese. You see the exact same attitudes to work in Korea and Japan. Confucianism is a powerful force in the region.
Suffice to say don't underestimate the work ethic and skill of Chinese laborers.
If you've seen enough people graduating into non-working class, or you have had yourself, that changes your perspective.