The post you quoted was a reply to my question of whether or not a gold tier holder (which grants +1 of up to 23kg of checked luggage) would be forced to pay at the gate, if he came there with an overweight "carry-on" (I have one that fits Aegean's size chart and I've loaded it with 16-18kg several times as a checked bag).
So if your friend with the 12+kg carry-on, who was forced to pay, was also a gold member, then this would have been a very useful piece of info to add.