This tactic has been used by the Chinese government in China to deny consular access to activists or sensitive prisoners. It is thus no surprise for Hong Kong to see this type of threat.
From what I know, the process to officially renounce one's citizenship is quite complex and requires an individual to personally visit the consulate to hand in a form. Formally we don't really have to worry, because if an individual is going into a Canadian consulate, there is a certain level of free will there. However, the Canadian government needs to take action to advocate for dual citizens and also maybe consider putting out public announcements about how an individual must go about renouncing their citizenship, if there is any information relating to individuals who are under duress requesting to renounce their citizenship.
In general, I think this is a rising concern and that Canada needs to keep a close eye on the issue.