Yes I doubt they could track that either. How would they even know that it was me? They would know that someone with my name had withdrawn money from a bank in the UK from a Thai ATM but there could be loads of people with the same name as me, could have been a tourist with the same name. So first off they'd have to contact all the Thai banks and check if anyone with my name had made withdrawals from foreign accounts using their ATM machines - but they still couldn't be sure it was me. My bank in the UK doesn't have my current passport number to confirm it is the same person and I would think client confidentiality would prevent my UK bank releasing details about me (date of birth etc.) to a bank in a foreign country.
Failing that, I could just send money from my UK account to my Thai gf's account and she could withdraw it and hand it over to me. Or are they going to tax Thais on money received as a gift from foreigners?
Given the number of foreigners and the number of financial transactions involved, it would be a massive undertaking. They can't even copy my name correctly from my driving licence into the computer when I renew my Por Lor Bor so tracking my ATM withdrawals from foreign banks that refuse to release any information about me would be a tough one.