I only know from friends living there, take anything I say as speculations, but what I gather is that they see open source as a technical advantage over starting from scratch, it's not a spontaneous movement.
it makes sense from the point of view of a country that has gained a leading position worldwide from accurately reproducing something that already existed.
judging from the number of Linux distro they are releasing I think they are pretty serious about it.
Chinese developers are the second largest group of contributors on GitHub
there's also a billion and a half of them, most of them don't speak english (edit: not all of the Chinese people are developers of course)
Anyway, GitHub itself it's not OSS and it's owned by Microsoft
AFAIK open source contributions are not usually rewarded in China by employers, but that's true in general in Europe as well