The DTA between TH & Oz is difficult & complex to read, but I think the bits on pensions are clear:
(1) Federal superannuation for former federal government employees can be taxed ONLY in & by Oz;
(2) All other pensions are at least theoretically taxable in TH even if already taxed in Oz (but taking in to account the taxes already paid in Oz, which may mean no tax to be paid in TH). So the old age pensions are assessable in TH but will often involve no further tax to be paid.