Atraditional story that explains a belief system, a natural phenomenon, or a world view of a group of people is called a

I believe the answer is: myths.

Myths tends to created when people in the past try to explain things that they understand without using scientific process, which resulted in a grand story that cannot be proven.

For example, in the past people do not understand why thunderstorm of created. Because of this, they made up a story on how a God in the sky throwing the thunders on Earth because He was angry at the people.