So the answer's right there. If the ATO online calculator can't give you an answer, you think a Facebook group can? Put it in writing. Get the ruling, then you know where you are
You've obviously not had dealings with the ATO. Phone calls are a waste of time. What they've told you is wrong as it goes against what is in their official policies. If the first guy had to go ask someone else that doesn't exactly instil confidence does it? You write to them, and get it in writing otherwise it's not worth a pinch of shit. You're better off to use the residency tool on the ATO website. I give you 100% guarantee you need more than citizenship. I've held on to my tax residency year after year for all the benefits it brings to me, so I make sure I'm solid with it.
You can be dual tax resident, but the Aussie DTA means Australian Tax Residency prevails, so you can shit-can the Thai Taxation, provided you have a permanent residence in Australia