Impeachment “is the process by which a legislative body levels charges against a government official” [1]. Standards vary from jurisdiction to jurisdiction. But since the decision is made by a political body, not judges, it is ultimately a political decision.
The article you've linked to says that in Hong Kong it requires 'serious breach of law or dereliction of duty'. I can't see how becoming unpopular would meet either of those conditions?
> since the decision is made by a political body, not judges
The article you've linked to says that in Hong Kong impeachment charges are investigated by judges.
A committee chaired by a judge investigates [1]. It then recommends findings to the LC. The LC, a political body, makes the decision to impeach.
> in Hong Kong it requires 'serious breach of law or dereliction of duty'
Practically speaking, based on history and the motivations of those involved, popularity figures into impeachment processes. Being unpopular doesn’t lead to impeachment alone. But pretty much anything could fit into Hong Kong’s “dereliction of duty” standard, for instance.
Is that what impeachment means? To remove someone because they've lost popular support? I thought impeachment was rather about charging a public official with some kind of crime or wrongdoing. Being unpopular isn't a crime.