The transition from arresting doctors to locking down cities doesn’t make much sense otherwise. You could argue they had motivation to arrest doctors talking about a natural infection if they thought they were spreading fear and disrupting lunar new year festivities, but going to locking down whole cities is about as fear inducing and disruptive as it gets. If that were the motivations for arrest, I’d expect more reluctant and less heavy handed mitigation efforts.
If this were a natural disease and the motivations were to control it as quickly as possible, I’d expect early doctors to be painted as national heroes/propagandized positively very early, similarly to the portrayal of the people that built extra hospital spaces early on.
It’s possible there were different officials involved that changed motivations halfway through, but the lab leak hypothesis offers a more consistent explanation. It makes sense that they would have tried to control the virus quietly if it were a lab leak/wanted to keep it secret, and that they would engage in drastic measures to control it when that didn’t work.