a DTA doesn't absolve you from filing a tax filing in the secondary location.
You will have to file in both Australia and Thailand. Even if you owe nothing in Thailand, that in itself is a huge pain in the ass. The Thailand tax calendar starts Jan 1st, the Australian tax calendar starts July 1st. That creates complexity. Then factor in getting documents translated into Thai and then getting those documents certified. Then hiring tax accountants in two countries to handle both submissions.
Then discussing DTA itself, you need to look at the DTA for each category. Some will give exclusive taxing rights to one jurisdiction, others are taxed in one first and then taxed in the other. For example, if you owe 30,000 in AU but 50,000 in Thailand, you would have to pay 50,000 in Thailand and then use a tax credit against the 30,000 in AU for your AU tax return after July.
The short answer is this <deleted> gets complicated at the very best, and costing you more at the worst.