Why the fluid will flow from a region of higher pressure to one of low pressure?

No. Gas flows from High to Low. This can be demonstrated by blowing up a balloon and then releasing the open end. The gas within the balloon is at a higher pressure due to the stretched rubber attempting to resume its original size. When you release the open end, the high pressure gas escapes to the low pressure outside of the balloon. Gas, like water, always seeks to achieve equilibrium.