I would immediately blame the attackers because there is no excuse for violence, ever.
This was a typical 13 on 1 Thai attack, doesn't matter what the guy said, or his past.
If he wasn't hitting them, there was no reason to hit him.
I'm guessing his gf was the wife of one of the attacking Thais, and the other attackers were the Thai husbands friends and family.
Don't ever go to her village, especially if you're a part-time bf.