From my experience living in Korea and the fact that Korea has one of the lowest productivity of all oecd countries, it is half-half.

A lot of the time is actually not "hard-working" but rather drizzling some work.

This is partly because you know it is expected that you stay long hours (and so you stay long hours without being explicitly asked) so you might as well just do your work slowly.

Also it is partly that nobody can work concentrated for such long hours. And a lot of time is wasted by people not asking when they are stuck with any kind of problem / task (losing ones face / looking incompetent problem).