Voltorb holds the #100 spot in the Pokémon Red and Blue Pokédex, and fans believe this could be tied to its design origins. The basic concept of Voltorb is a Pokémon that looks like a Poké Ball and will punish those who bother it by blowing itself up.
According to the various Pokédex entries for Voltorb across the Pokémon series, it was discovered around the time when Poké Balls were invented. Pokémon has never established exactly how long some form of Poké Ball has been around, but the series is getting its first prequel game in 2022, Pokémon Legends: Arceus. This game is set in an ancient version of the Sinnoh region, when Poké Balls were made of wood and powered by steam. It's possible Voltorb didn't exist until the modern, electronic Poké Balls were invented.
The Pokémon world has Ghost-type Pokémon that can possess regular items, including the electronic devices possessed by Rotom. While not a Ghost type, Voltorb seems to be in the same category as these, as it's likely inspired by a Japanese myth linked to its Pokédex number.
Voltorb Origin Theory: How A Poké Ball Came To Life
There is a spirit in Japanese folklore called the tsukumogami. These are generally understood to be household objects and tools that gain sentience after a century of use. According to folklore and travel blog The Willow Web, the nature of a tsukumogami's spirit reflects how the object was treated in the past; it can be cruel to those who used it poorly. It's likely Voltorb was inspired by these spirits, as it's number 100 in the Pokédex, reflecting the 100 years of existence required for a tsukumogami to be created. This seems to be a choice made on purpose, since each Pokémon's entry into the first games' files didn't determine where it was placed in the Pokédex. Rhydon, for example, was the first Pokémon programmed into the games, but it's #112 in the Pokédex.
The developers of Red and Blue likely didn't have a timeline in mind for the Pokémon world as a whole when creating the initial games, so it's possible Poké Balls had been around for a century at that point. It wasn't until Pokémon Legends: Arceus that an older design for the Poké Ball was ever shown in the games, which suggests a new version of Voltorb from ancient times could also appear in a future Pokémon game.
Source: The Willow Web