I am not aware of anything special that happened that evening, though I would often describe the economy check in area as very busy, it has always seemed reasonably well organised - even when the queues snake round the corner.
The whole area is about to undergo a re-vamp -
see here for brief details.
I think the red and green stickers and the people in polo shirts are dealing with the unpopular APD (Air Passenger Duty), which is explained
here. Though I stand to be corrected on that one.
Some friends of mine flew out to Delhi that evening, so I may find out more when they return, if no one else chips in before then.
Nick