Github and Npm are both used in China all the same. I don't know about firewall restrictions, many chinese companies publish directly on Github. React is the most used in China in polls as well (stateofJS), with some of the biggest names and websites using it. If China would be excluded in these stats, that would impact Reacts outlook more for sure, any exception one could make would directly affect React in the same way.

As it stands npms numbers coincide with all the other sources you could pull: projects on github, tracked project dependencies, size of eco system, job market, etc.