This statement confused me, so just to be clear, this video: https://www.youtube.com/watch?v=ldNnKVGxabA demonstrates the correct way to breathe right?
Wrong - pull in stomach (breathe with chest)
Right - expand stomach
When we breathe, first the lungs fill up, as adults we exhale at this point. We should continue breathing until full lung capacity i.e until it pushes the diaphragm down which in turn pushes the stomach giving a sense of pot belly, if you have a pet or a child notice their stomach while they breathe.
There seems to be little confusion about chest/stomach breathing. We draw air with lungs which reside in the chest, its just that we are training our body to take deep and longer breaths we get a feeling that we are drawing with stomach
As PG says one needs child like curiosity, we need to child like breathing :)