A regular person in Argentina around 1956 doesn't have many reasons to distrust the authorities. But if you are an old person in China, would you really believe that this one time the government really does have your best interests in mind?
They lived through the cultural revolution, the famines, the civil war and so on. Maybe they figure they'd rather take their chances with covid.
Old people in China tend to be more trusting of the government than young people, in my experience.
People who have lived from before the revolution to today have seen a complete transformation of society. They don't connect the current government with the Cultural Revolution, because the people who took over after the Cultural Revolution (like Deng Xiaoping) had themselves been persecuted during it. They tend to see the history of China during their lifetimes as one with many struggles and hardships, but ultimately of success.
Vaccine hesitancy has much more to do with traditional medical beliefs, which is why Taiwan, Hong Kong and Singapore have faced the exact same problems with convincing elderly people to get vaccinated (there's also the fact that all these places did a vastly better job than the US or Europe of protecting their populations throughout most of the pandemic, meaning that old people didn't feel the same urgent fear that they might get CoVID any day).
They lived through the cultural revolution, the famines, the civil war and so on. Maybe they figure they'd rather take their chances with covid.