I think it's less that the muscles are different, and more about body fat percentage and maybe distribution. You could have the strongest core in the world, but if there's a layer of fat on top of your abs, they won't have this visible definition.
Also... Really rare to have boobs that big AND such low body fat, but all sorts of women get implants.
But then why does it sound so different if I take my thumb out of the motion and just slap the same spot with my finger?