Not suggesting you were having a go at the other passengers, as you say its a common sense thing, your bag is 4kg over but you weigh 20kg less than someone with a 2kg under bag. In the big picture it doesn't matter but the staff need to have rules to work to and I have seen staff get surly very quickly when going down the but look at the size of him route.
Know the rules, a lot of things can be in the hand but don't count as hand luggage, and being nice and polite to the staff goes a long way.
Again not directed at you but general advice to all.
I know airports and airlines have rules but what annoys me is that some seem to go out there way to catch you out and charge you extra. Spell a name wrong when you book and then try to change it... kerching. Turn up with hand baggage half an inch to long.... kerching. Ryanair are one of the airlines appealing about some new guidance allowing more hand baggage allowance and the owner has made it clear that staff will be incentivised to raise more money in such ways.