I think it's a tropical thing. Hoenn had plenty of unrelated (in that they do not evolve into/from one another) pairs of similar Pokemon. Plusle & Minun, Volbeat & Illumise, Lunatone & Solrock, Lati@s. There's also the dissimilar pairs, Mawile & Sableye and Zangoose & Seviper.
It could be split evolution, it could be trade evolution. Or it could be two species looking similar but being from different areas, like if East/West Shellos & Gastrodon were different species.
>Grubbin loves electricity, which is why it can be found near power plants and substations.
Either way, they're definitely close to each other.
