The Chinese propaganda/education/censorship system is set up to accommodate all levels of disbelief of propaganda - that's built in to the propaganda, too.
So there is the official line, then there's the unofficial official line - which is generated by being pessimistic relative to the official line.
If the official line is that 7 people died in a disaster, rumors will float around that it was really 70, and people hearing that will feel content, cause hey, 70 people is not a lot to pay for 20 years of good economic development. Since they're anchored by the official line, suspicions never jump to 7000 people died, 20k people had their lives destroyed, which may be the reality.
It's the same with corruption - if an official gets busted for embezzling, skeptics guess that his wife is still overseas with millions, he had a couple cars, mistresses - but now he got his due and will never get out of jail. But they never guess that he was the equivalent of a mob boss in his city, had peasants disappeared, isn't even actually serving jail time, etc. (because that story would never, ever be mentioned again.)
So, rumors slightly inflating the official line are allowed, even encouraged, since they strengthen that line. But rumors showing that the official line is totally fake are destroyed - any reporter who brings one up can look forward to a life in a small town working in a factory, no education for their child, and nobody would ever hear a word about it, anyway.