This is the kind of stretching that isn’t good. When overeating becomes a habit, your stomach wall stretches. Stretching of the stomach results in it taking more food than previously for you to feel full.
Did you read it? Also, none of your links are talking about the expansion of the stomach wall or the stomach muscles. They're all related to dieting - and shrinking the stomach by not eating - not what we're talking about. The size of the stomach is, apparently, mostly conditional on the smooth muscle tone. Overeating can stretch or tear those muscles, and undereating consistently can cause them to firm up, requiring that they be stretched again before you can eat as much food as you may have before.
That's a volumetric change in the capacity of the stomach based on your eating habits.