The entire island of Niihau is owned by a pair of reclusive millionaire brothers (the Robinsons), who run the island as a traditional plantation where the locals are more or less serfs. Electoral results there should be seen as reflecting the interests of Keith and Bruce Robinson alone. They are environmentalists but also strongly anti-tax and generally anti-government (both the federal government and the Hawaiian state government).
Interesting. I don't know if it's fair to say the locals are practically serfs, as it seems they are just living a traditional Hawaiian lifestyle. Either way, you're probably right that the Robinsons told them to vote Trump. Niihau is a very strange place.
