I also first heard about it on AN (or was it TVF back then?) It came up in an article in the Thai Enquirer which included the sentence:
'Also exempt will be those who have been taxed in a foreign country that has a standing Double Tax Agreement with Thailand'.
This was dismissed by the afore said as ML not being an official statement and so the rumour perpetuated. In the 14 months since that was published, I haven't read one single article that contradicts that sentence, so AFAIC the taxing of us pensioners is still an unsubstantiated rumour.
I agree with with earlier posters such as @Jingthing. Stay well away from TRD offices and tax advisers who are seeking to plunder your hard earned retirement pots.
Thai Enquirer September 18, 2023