Is there always turbulence over China?
China is well known for having very strict air traffic control, who often are reluctant to give pilots the flexibility to deviate around bad weather or try a different - smoother - flight level (as I've experienced first-hand). That can lead to aircraft in Chinese airspace encountering more turbulence than in other parts of the world.

Secondary to that, China can get some nasty weather: Particularly in the South. Compared to Europe they'll have more thunderstorms, for example, and that can lead to increased turbulence. This image here gives an overview of the number of lightning strikes around the globe. Aside from a few patches in Italy, China has more lightning - and hence more turbulence due to thunderstorms - than anywhere in Europe. As you mention, the mountainous terrain in some parts of the country also has an effect, although you get that in Europe too.