He may be half Thai, but may not have a Thai passport, maybe to evade military service or its hard to get if the father is Thai ,its easy if the mother is Thai the embassy told me this when I got my sons Thai passport. But we don't know if he is of Thai extraction, the name sounds Thai.
If the mother was Thai the embassy excepts the birth certificate translated into Thai, but they say if father they want DNA sample of proof. Then the parents might have parted ways, who knows maybe some one will through some light on this.