War rationing led to this food becoming known for exploding.
Sausage is already known for being a mash-up of whatever meats are handy. Even top-quality sausage only has about 80%; the rest are spices and other filler materials.
During World War II, England was struggling to keep up with the needs of fighting a war. Rationing became an important part of this. As food became scarcer, butchers were making sausages with as little as 20% meat in them; the other 80% was mostly water.
For people that didn’t know any better, the sausages were lethal projectiles when you cooked them. This is why British people often refer to sausages as bangers. Fortunately, once rationing ended, butchers started using meat again; however, the name stuck.