Your answer to his question is irrelevant. Just because he has paid tax in Singapore doesn’t exempt him from Thai tax under the double taxation agreement. Which is what his question is implying. 180 day rule still applies in thailand for tax resident purposes.
Irrelevant. He’s Thai tax resident if he’s been in Thailand for 180 days or more in a calendar year. He needs to file a tax return in Thailand if he has brought in assessable income in 2024 (over 120,000 baht for a single person).
If you’ve spent 6 months out of thailand and I was the immigration officer, I’d be asking a few questions…First one being please show the contract with the school.