Well i don't claim to be an expert in the scientific explanations, but i have experienced it first-hand (or actually second-hand, since it was with my partner).
She used to eat just average meals normally, but at special occasions she definitely could eat quite a lot, it was just pretty hard for her and she definitely felt that.
Now over the years she has gradually been snacking more and more to the point where she is able to eat regular sized meals as a 'snack' so to speak and not feel particularly full. Her uppermost limit probably still isn't insane, although it's definitely more than it was, but it's the smaller meals and the hunger where it's noticeable.
Basically regular sized meals don't make her feel full anymore and as a result of that, just small snacks or average sized breakfast leaves her hungry, while in reality it would probably be enough. So the stomach doesn't necessarily stretch out a lot more, but it gets used to getting stretched a bit. That's how i've experienced the stomach stretching phenomena.
5 years