Katana,
As far as I know the police only gather all the evidence and that gets sent to the attorney general (or whatever they get called in Hong Kong). It is they that then decide what charge to lay - be it murder or manslaughter.
Murder is a more difficult charge as it requires not only the act of murder BUT also the intent to kill at the time of committing the crime.
It may be difficult to prove that during a brawl they intended to kill the man.
However they will take the view of what a "reasonable man" would have expected the outcome of this brawl to be - Grievous Body harm or murder.
All that being said - The man is innocent until proven otherwise!! So let him have his day in court.