I'm no expert on herons, but that sounds reasonable to me. The leg and bill colours are wrong for white phase reef heron (I don't think the bill is heavy enough either), and the same applies to plumed egret. Also obviously not a white heron, cattle egret or little egret (going on build, gape, and bill/leg colour), and looking through my Asian and Australian bird books there's nothing there that matches either. Those yellow legs are the real kicker. The build (especially those short legs) looks reasonable for white-faced heron, and given that it's the commonest heron in the area it's probably your best bet. Very cool looking bird though.