A bad explanation is unspecific. You can change any or all of the details without destroying it.
Examples of bad explanations:
- Thunder is caused by Thor's anger
- Day and nights were created by God dividing the light on the first day of creation
- Summer is caused by Persephone's annual re-uniting with her mother Demeter.
In the above examples you could change any of the variables and the explantation would make sense.
- Thunder is caused by Zeus' anger
- Day and nights were created by God dividing the light on the last day of creation
- Hades is distracted when Persephone leaves, and forgets to cool the planet.