I would guess it's a mistake. They copied the text over from the OA visa email or something. Remember immigration isn't that familiar with renewals of this visa yet.
If you're coming to Thailand, get used to things not making sense. And get used to different offices of the same branch of government 'interpreting' laws and regulations differently.
it's my understanding that Thai taxes are based on money remitted to Thailand only, and not worldwide income, but they are considering adding the worldwide income aspect.
Anonymous participant to the local immigration office where you're staying. When I got a new passport, I actually paid an agent to do this. I don't usually pay an agent. They took both my passports down and had the immigration office take care of it.
he simply asked an immigration officer what would be required for extending in country. The officer replied that you'd have to again show financials and other documents and suggested briefly going out of the country was a better alternative.