When i resided here in the 80's and you had stayed more than 180days to leave you had to have a tax exempt certificate. If you proved to the revenue dept your income came from outside you got the certificate free othewise it was i think about 2500 baht fee for the certificate to leave the country.
Anun Pryachum the best PM Thsiland ever had cancelled it when he became PM.
So this tax idea for foreigners is not good but it's not new.