I just read up on it. There are several visa types that require insurance. And there are many situations that do not legally require health insurance if going to Thailand. If you can point to a law that says different, I'm happy to correct myself.
You are not required to have health insurance to live in Thailand. The non-O doesn't require insurance on renewal. The non-oa has an insurance requirement, and perhaps others, I'm not sure.
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.