There is a great deal of self-censorship in Chinese entertainment. Whether it's spelled out or not in a policy guide book is irrelevant. The reality is that censors have a lot of power and, unless you have strong government connections, it's not worth putting anything risky in your work, because you're not going to win a fight against government censors, regardless of if you have logic and reason on your side.
As a consequence, creatives try to steer clear of controversial topics, be it graphic violence, sex, horror, strong critiques of society, or especially, politics. This is the reason you get so much light-hearted romance, fantasy, and comedy in Chinese fiction - because those are the safest genres. This is not to say you can't make anything else, it's just that you take a huge risking making them, because censors could threaten you at any time. So only the most daring directors with high investor trust take the chance.