@dr_shadow has already talked on this and it is perhaps one of the worst aspects of China's dictatorship. You CAN'T leave, passports in China are issued only to well off businessmen and government officials that that presumably are also checked by the government for political reliability. Just leaving China is not a choice, you are FORCED to live there, even if you actually had the means of moving somewhere else.
thats factually false
This sounds like North Korea level. Also, it seems unlikely, and this is why. China is a very large country. In order to prevent people from leaving, the government would have to use a lot of resources to keep citizens with both the land borders of the nation and to keep people from getting on planes or boats.
the only way someone isn't allowed is indirect like they can't afford the passport, which let's be honest how many people in western countries can afford passports?
"Before 1978, China was pretty much closed to the outside world. Few Chinese citizens were allowed to travel to other countries. Those who did were either businessmen, government officials, or students. Taking a pleasure trip abroad was unthinkable unless it was disguised as a legitimate trip. All that began to change in the 1990s when China adopted a unique tourism policy. China’s Approved Destination Status (ADS) Policy allows overseas pleasure travel by its citizens in tightly controlled groups and only to countries (and territories) approved by the government. Tourist destinations around the world hailed this move. Imagine the world’s most populous country of more than 1.3 billion people spreading its growing wealth around the globe! Lost in the euphoria was the policy’s big limitation: Chinese citizens were not able to go where and how they wanted."