This way of breathing is something between the “corset” and athletic breathing.
It might look similar to the athletic breathing, but when you’re breathing this way, your abdomen is way too tense, thus restricting the chest and diaphragm movement and lungs from expanding into abdominal cavity, resulting in chest breathing.
If you are a “corset” breather, you restrict your diaphragm movement for beauty purposes, but in this case you do it to kinda protect yourself. Psychologically, the stomach is a very sensitive body part and in animal world, an animal lets someone touch it only if they completely trust them. People who are always tensing have put themselves in kind of like a “prison”, and it’s very hard for them to get out of it and learn to relax and just be. They are often very tense also psychologically, they are always ready to “fight” and defend themselves, and don’t want to open to others.
Many of the people who breathe this way are the ones who just want to get a six pack at any price and are using every minute to get closer to that goal.
Singing while being so tense is a difficult task, usually it comes out very forced. Re-learning to relax your abdomen is a time consuming process, but definitely worth it.