China's low death count is exactly what you'd expect for a country that had a severe lockdown early on, and which has not had significant community transmission since.

Beginning in late January 2020, there was a strict lockdown throughout China. In Hubei, people were essentially told not to leave their homes, food was delivered door-to-door, local volunteers went around checking people's temperatures at home and sending sick people to hospital or quarantine, in order to prevent even family members from infecting one another. The virus was starved of hosts and driven to near extinction in the country.

When China opened up again, there were sporadic cases in some cities, which were finally dealt with through mass testing campaigns. In Wuhan, for example, the government tested nearly all residents (about 10 million people) over the course of a few days in June 2020.

There have been a few outbreaks since. China has very strict quarantine rules, but the virus somehow finds a way in every few months. Most recently, someone who was infected walked over the border from Myanmar, without being tested or sent into quarantine. When these outbreaks occur, the government tests nearly every person in the affected region (the newest twist is now that there are vaccines, the government is vaccinating every person in the affected border town - in previous outbreaks, they would have just done PCR tests on everyone). When you have the resources of a massive country to throw at a small, localized outbreak, you can actually contain it.

So the basic situation is that China had one major outbreak in Hubei province early on, but that the virus has been nearly completely absent from the country for more than a year now. China's death toll is exactly what you'd expect for an outbreak in one province that infected <5% of the population of that province before it was stamped out.