They always do that even having a proper visa. My uncle is married to a Thai lady for 20 yrs now but still gets questioned everytime they comeback here from vacation in Sweden. And his nephew is studying here and have an Education Visa was held and denied entry at Suvarnabhumi but then allowed to enter after he was fined 7k baht with no receipt! And a friend of ours was held and not allowed to enter even having DTV visa and later on he was allowed to enter after being fined.
So yeah it's a thing now in Thailand, it can happen to anyone even if you have a proper visa or just a tourist! 🤦🏻♀️
Even if you have a long term visa, some immigration officers will stop you entering the Kingdom. That happened to my boyfriend after a month vacation in Sweden last year even he have ED Visa that will expire after 1 yr and they want him to fly back to Sweden. We were so worried so we called the school and they talked with the officer over the phone and IDK why one officer was messaging my man to send him 7k baht on his account so then he can enter the Kingdom. This happened at Suvarnabhumi Airport.
Realy silly. Them creating this new DTV visa and their officers have no full knowledge of the implementation of the visa. Now it's giving visa holders a hard time even just extending stay via local immigration. 🤦🏻♀️