Yeah. According to Chinese user speculation (before Chinese forum was removed), this is possibly because of China wanting to promote their crappy WeGame.

The Chinese say, China blocked Google to promote Baidu, blocked YouTube to promote Youku, blocked Facebook to promote Weibo and now Steam is the next sacrifice.

Some also say its due to people criticizing the Chinese government openly.

I believe this also affects other aspects of Steam not just chat/discussions, such as trading, the Steam Market, Steam Workshop and other online features, which is unfortunate. I would classify it as a straight up "dick move" by China.

The great firewall of China