Very often when a completely rational, non-abusive person is blowing an absurdly tiny thing completely out of proportion, they are not angry despite of the thing being so small, but because it was. The source of the anger isn’t directly proportional to the cause, but inversely.
From their perspective, it would have taken you such an extremely small effort to not do/say/avoid/forget the thing that it is insulting that you would not trouble yourself to not do it. In a way it’s as if you went out of your way to let the offended party know that you do not care about their wishes or preferences out of principle.
Telling someone whose anger is inversely proportional to the size of the slight that the matter was not a big deal is only pouring more fuel in the fire. They are angry because the thing was not a big deal.