Well truth be told I was grounded in Kai Tak for 10 hours about 20 years under similar circumstances. The original departure was like 21:00 but the whole airport was fogged in, nothing took off til 08:00 the next morning and we weren't allowed off except for breakfast (which CX provided coupons for) - we saw for ourselves how full the terminal was. We then had another 9 hours flying ahead of us to make my only night landing in Australia from Hong Kong as a child.

It's not new, but is it right? At that time neither me nor my mother thought much of it, taking off at 08:00 meant my brother could drive us home.

What is best for CX/KA might not be best for passengers' all the time. The CTU passengers probably had a different set of circumstances to me - not prepared for an overnight flight (probably expecting to sleep in home/hotel at Chengdu), not given hotel or wash opportunities, no meal coupons, probably they were none too pleased to be kept in the terminal for flying off at 08:00 - a later departure is most likely more comfortable for them.

Isn't some comp payable under these circumstances? And if yes it shouldn't require passengers whatever their ethnicity to threaten force to make it happen.

(Note that some tourists may not be allowed to re-enter HKG - I've seen this happen when a HX HKG-HAN flight of mine was MXed and a Vietnamese tour group had to be housed in Plaza Premium overnight rooms whilst we get housed in Park Lane).