Yes that was my point, thanks academic.

Its really at the Crews discretion. After reading your post further I am inclined to think this Purser was upset about having to work. Sometimes down route Crew get called off their layover to operate - perhaps this Purser was thinking since he had been inconvenienced so would everyone else. Not really acceptable IMHO.

There could be various reasons for this, sometimes even something as little as a suspicious virus going around in HKG (as an example for this trip) can cause the Crewing department (or the Captain) to instruct Crew to take this precaution. An explanation to the passengers doesnt hurt though...