Just for info, the opposite happened at Bucharest on a DOH-OTP-BUD service, and it was announded by the cabin crew. Only passengers for Bucharest were allowed to disembark, and, on alighting, their boarding passes were checked before proceeding to immigration control and baggage reclaim.
I don't think QR had traffic rights between OTP and BUD, and as there were no embarking passengers, probably wanted to depart as soon as the OTP passengers had disembarked and their luggage unloaded.

I don't know why its the opposite at Singapore. What happens at Bangkok with the DOH-BKK-Hanoi/Saigon and v/v services?

These stops are shown as 'technical', but aren't. That phrase is misleading. 'Technical' refers to operational reasons for a stop, such as re-fuelling or crew change. These are traffic stops.