“He has never been unruly," Jittra Songlong said on Thursday.
"He is well behaved and has never made trouble for the family. I am very puzzled by his arrest.”
The 42-year-old mother, who has not seen her son in two years, was speaking from her family home in tambon Nai Kuan, Yan Ta Khao district of Trang province.
Mrs Jittra said her son left Thailand to study at a religious school in Swabi city in Pakistan in 2013 and they regularly talked on the phone. He told her he would return home for the first time on Wednesday.
Mrs Jittra said the teenager did well at school and had never had any problem during his stay. He planned to finish his studies in Pakistan in the next six years and return to Thailand to work as a teacher at an Islamic school in Trang or elsewhere.
She said police officers, provincial authorities and Pakistani embassy officials had visited her after the incident.
Mrs Jittra’s son was with four other Thai students as they were boarding a Thai Airways International (THAI) flight TG 346. An X-ray security machine found a 9mm pistol and ammunition in his luggage.
The five Thais, whose names are withheld, are now being held at a police station in central Lahore.
Deputy government spokesman Maj Gen Sansern Kaewkumnerd said Pakistani security officers had not yet allowed officials from the Thai embassy to meet the students, but confirmed that all are safe.
“A preliminary inquiry by a security agency did not find any link or behaviour that shows a relationship with the insurgency movement in the three southern border provinces, or any other group,” Maj Gen Sansern said.
He said authorities would follow the results of the investigation into the incident by Pakistani police.