While China’s WADA positive test rate is indeed low, it’s higher than the Chinese anti-doping agency (CHINADA) positive test rate, by quite a significant amount, which may suggest that the national agency aren’t policing doping as closely as WADA. The USA’s national anti-doping agency (USADA) has a higher positive test rate than WADA’s, again, by quite a significant amount. Additionally, WADA has significantly higher sample rate in the US compared to the sample rate in China - despite the fact that CHINADA has a much higher sample rate than USADA.
My point isn’t that the US is better or more honest at handling doping than China, just that the analysis of doping test rates has quite a lot of variance, and it’s difficult to draw meaningful conclusions from them.