Have you ever wondered why old people think Pokémon are called "Pokemans"?
Today, the Pokémon series is a household name in the English-speaking world, but in 1997, Nintendo and Game Freak were still working on the localization for the games that would come to be known in English as Pokémon Red and Blue. Game cartridges with in-progress translations were produced in limited quantities for use in focus testing, which was carried out in a variety of Western test markets.
It is likely that your grandpa acquired the term "Pokemans" from participating in one of these location tests, although Nintendo's non-disclosure agreement would prevent him from ever discussing his experience as a focus test participant. Luckily, a localization test ROM for "Pokeman Red" has recently leaked, which confirms that the name was in consideration by the developers at one point.
The localization test ROM is copyrighted material, so it can't be legally distributed in most territories, but if you have a legally-obtained North American Pokémon Red ROM, you can use this IPS patch to convert it to the Pokeman Red ROM.
Alternatively, you can play Pokeman Red right here in your browser by selecting your legally-obtained North American Pokémon Red ROM in the file chooser below. The controls are listed here.