PIT = Personal Income Tax. Your UK income is subject to PIT and paid to the UK government via the PAYE system. PIT is one of many forms of withholding tax charged at source.
glad you accept that you are taxed wherever you are tax resident. Countries do not declare you a tax resident, many countries have qualifying criteria you must satisfy in order to automatically become tax resident, centre of economic interest being one such requirement. Thailand does not have this criteria. Thailand only has a residency requirement therefore the question of whether someone has or has not a Thai bank account is irrelevant for tax residency.
entry requirements are defined in law. Visa exempt entries have entry requirements of holding an onward ticket. During covid all visa entries had an entry requirement of a covid free ATK test. There are no entry requirements for DTV holders.
Anonymous participant whilst there are no entry requirements for a DTV holder every entry regardless of visa type or visa exempt is at the discretion of an Immigration Officer.