Why would you think it's difficult ? If you go to the correct office it's a 5 minute task. Most people don't bother as it's not required to file tax at this point and who will check you have filed or not filed. Like most things in Thailand farang think it is such a difficult thing like a motorcycle licence most done bother because they must produce the right documents but again it's so simple
The post sounded like he came in on one flight and was stamped in then proceeded to Air Asia check in. Whatever they did sounds strange. Like the IO was making him blush he sounds nqr
You tell the story like a victim. So what any country that has a DTV is welcome in Thailand. Domestic flights in Thailand don't need to show a passport so what are you showing them Air Asia or any airline don't care about your visa just you have a valid ticket to travel.