Voltorb is a weird fucker
Some pokedex entries:
"It was discovered when Poké Balls were introduced. It is said that there is some connection."
"The link between that sighting and the fact that this Pokémon looks very similar to a Poké Ball remains a mystery."
"During the study of this Pokémon, it was discovered that its components are not found in nature."
People in the pokemon universe just accept that

Homestar logic.