Their analysis is always remarkably detailed.
Their analysis was worse than usual this time. They kept saying there wasn't any tall grass but the overview of the island clearly shows tall grass. They thought the trainer's house was on the beach, but that house is blocked off by tall grass so obviously that isn't it. If I had to guess, the game starts with the trainer getting off a boat in the city based on Honolulu and then hiking to their house in starting village along the route that doesn't have tall grass. Then, once the player meets the professor and gets their pokemon, they return to Honolulu but are forced to take the north fork of the path that has tall grass.
They also didn't point out landmarks from Oahu that the island has versions of, such as Diamond Head and Sacred Falls (really surprised they didn't at least mention the giant waterfall).
The also thought the professor's assistant might be the trainer's cousin and didn't talk about how "cousin" is a common slang term in Hawaii.
i bet the whole game is only on that island. if you're lucky post game will be another island like the frontier was
This isn't likely. The island is very small. It only has about 3 routes, 2-3 towns, 2 pokemon centers, and a few caves. I can see there being maybe 8 islands; one for every gym. Maybe have 2-3 gyms on the main island.