Indeed PBOC investigation was to look into possible market manipulation according to the statements posted on the People's Bank of China's website. But the reality china still have any impact for bitcoin and 'playing' with bitcoin. Your opinion isn't fully true if said that china are NOT HAVING power.
Manipulation and everything was being caused by high frequency traders exploiting the zero fee platforms, and thus could recklessly make the price go up and down to their heart's content. In fact, it made them look far more important than they actually were if you look at the situation now. Chinese exchanges are now nothing more than what western exchanges are. I even tend to say that they are
less than western exchanges, since a few of them (previously the undisputed nr1-2 with millions
BTC in volume every day) fail big time to generate decent volumes.