I agree. I am living in BKK and came to Chiang Mai for weekend so have been watching the air quality for a while. BKK air has been terrible and Chiang Mai seems to follow the same levels. Go for safe air.
It must be a PCR test. I have never seen specifics Re the sampling. My tests in ASQ were throat only so assume this is ok for Thailand. In Australia it is a nose and throat swab.
A funny but frustrating story. You needed to read all the instructions. I did mine in Sydney and also needed permission to leave the country. Started Sunday and had COE on Friday morning. Best to actually drive to the embassy. Get to talk to the people and they help. Eg. You can start your registration for the COE before you have your Visa. Get the ASQ and insurance ready. Don’t miss any steps. You don’t need Fit to Fly until you are at the airport.
When you teach Thailand the process is rigorous to check all paperwork.