From Wikipedia This Article is part of the Thai Motor Vehicle Act
Australia does have a treaty with Thailand - Geneva Traffic act 1949
Section 42
Anyone who wishes to drive a motor vehicle on public roads must possess an appropriate driver's license. The driver must carry the driver's license and a photocopy of the registration book and show them to competent officers upon request. This does not apply for those who are learning to drive a motor vehicle according to the provision of Section 57.
If the driver is an alien who doesn't have an immigrant visa, he may drive a motor vehicle with a driver's license specified in the Section 42-2. In such a case, he must carry documents specified by the treaty between the Thai government and the government which issued such driver's license, and show them to competent officers upon request.
Section 42-2
In case there's a treaty between the Thai government and a foreign government regarding mutual acceptance of driver's license, an alien who doesn't have an immigrant visa may drive a motor vehicle with a driver's license issued by such a foreign government, or an automobile association authorized by such a foreign government.
_---------------------------------
So this comes down to the "fine print" in the 1949 Treaty, it appears.
I'll try to figure whether that's just your licence, or accompanied by an IDP