I think he wanted you to bribe him, he gave several clues also,(1) excess baggage, didn't get a good result so (2) he decided to try again when you were boarding and instead he got nothing out of it but made you and your partner pay excess on another carrier and hotel fees.

It's just my interpretation, but what would have happened if you did bribe him? I agree that this is very unacceptable that since you told him you had onward connections to mainland china, he should have allowed you onboard the aircraft, it's his own fault for not detecting the issue earlier, not yours. You have every right to fly, legally into HKG. You should at least look for compensation with the airline in question.

MH ground staff can be abit off tune sometimes, but their cabin crew are always excellent!