In no way am I condoning the teacher's actions but, there must be more to this incident.
Firstly, I'm surprised there is no video evidence. Surely the students would have taken the opportunity to get their phones out.
Secondly, was it only that one student? As a teacher of over 20 years, and one that has quite possibly taught at the school in question, my experience tells me that Thai classrooms can be brutal. The lower end of the grading spectrum is very demanding. Students paying no attention, not doing what's asked, doing things they know are prohibited, noise, loud noise, disrespect. General disobedience. With often 45+ students in the room, things can get heated. The no fail policy doesn't help as students are aware they can behave badly and still get a pass grade.
As I said, I don't condone the teachers actions. However, I think a good look at the bigger picture within that classroom and mitigating circumstances would be a good thing.
I have seen teachers leave classrooms in tears. Broken by the behaviour of the students. Were the students punished? No.
Counseling for teachers, training on behaviours of concern and more effective ways to discipline students required.