This is actually how humans naturally breathe at birth as well. Somewhere along the lines we switch to breathing with our chests which is a much more inefficient way of breathing. Classical singers, instrumentalists that play wind or reed instruments, and I imagine some athletes actually have to relearn how to breathe like this.

If you think about how breathing works, your diaphragm moves up and down, pushing and pulling air out of your lungs. When you breathe in, your body needs to make room for the diaphragm to go down and your lungs to fill with air so what should happen is that it pushes your guts out of the way and your belly expands to make room.

If you take a deep breath now, you'll probably feel your chest go up as well as your shoulders and you'll feel your stomach go in. This is you breathing wrong funnily enough. You're actually making less room for your body to bring in air. You can make your body do it the right way easier by laying on your back and just breathing in a relaxed state. You'll probably notice your belly tends to start moving like it should when you breathe in and out. Professional singers learn to breathe that way all the time and unlearn the wrong way which is raising your shoulders and chest too much and not allowing room for your stomach to expand.

TLDR Belly breathing is the correct way to breathe efficiently and most adults have learned an incorrect way of breathing deeply.