The right of free transit have been denied in every country with enough infections, why would you particularly demonize China for it? You are in quarantine, you cannot leave, period.
The drones seem if anything quite a lot less privacy-intruding than other possible measures, assuming they're just wandering around looking for people without masks. It would be embarrassing to be on the receiving end but with no real lasting effect or privacy loss, which is ultimately a pretty ideal result on a societal level.
With complete lack of freedom and privacy, you can achieve a lot. They're doing better than any western country would: https://www.wsj.com/articles/how-china-slowed-coronavirus-lo...