You probably qualified under economic ties, but it's more than just citizenship. The ATO website has a tool for determining if you are tax resident. There's also a new formula being introduced within the next couple of years which apparently will make it easier to determine
Not if you retain tax residency in your home country. For Australians anyone. We've got a pretty water tight DTA. We can only be taxed in one country. Your country might be different
The mugs who are so excited to get a tax ID and file a Thai Tax Return have total freedom of choice. Those of us who have already paid taxes elsewhere and retain tax residency in another country will choose not to do so.