First off, according to the airline, the ac was in cruise.
Perhaps it is best to leave off all of the comments regarding Chinese passengers.
Aussie Airlines that enforce the seatbelt sign? I am certain, having extensive experience flying around Oz, that there are very, very few.
Flights around China and other countries are much different, ever seen a pax have a goat as carryon? well it happens (and it okay on many flights)
Regarding the pax, ever been on a Ramadan flight?
Sorry, but it IS the crew job to educate and enforce, which in reality, I see very little of. When was the last time when the SB sign came on, the cabin crew went around and observed/enforced the SB requirement?