Does China have a motivation to be honest about their figures? Did they a year ago, or two years ago? Even if they're honest now, no doubt they were first hesitant once the cat (COVID-19 in this case) got out of the bag?
Back when COVID first came out, local officials on the ground were hesitant to bring attention to what they thought was a minor problem at the time. Even when the deaths began piling up, they were still trying to hide from the central government, and even then, plenty of information was leaking to the outside, everyone knew something was up even if they weren’t sure what it was. However, once the central government got involved, well, any chance of deception at the local level was off the table. The central government doesn’t really have a boss to hide things from, so in that case, things work out for transparency (but, ya, if they thought they could hide something, they would be tempted to for face reasons).