It actually started as opposition to an extradition bill that has since been shelved for now (for obvious reasons) and then transitioned to a call for full blown democracy and accountability of the police forces - who are now under the control of the Chinese government.

I think (rightly so) they are more afraid of the Chinese government coming in and strong arming their population like they do to their own population. The treatment of dissidents and the possibility of having to deal with the Chinese government in any fashion is something that makes the entire population nervous.