If you ever end up, through whatever sort of unfortunate event, being accused of something, you'll appreciate very much the idea of needing your guilt to be proven beyond a reasonable doubt. Although this guy appears to be a genuine scumbag, the evidence is not as clear as one would hope in order to convict this guy (on the charge of physical assault/battery). I don't know how a juror/judge could convict on the evidence that we've heard here. It is plausible that he could have slipped and struck her by accident that way, and the real time apology stating as much lends some credence to the idea, even if one is reluctant to believe it because of his character. The fact is, that could have been what happened. It is not beyond a reasonable doubt. His inability to control his anger and ego doesn't make that an implausible event. But other than the disputable accusation of kicking her, I don't see why he shouldn't be charged with assault. There may be no battery, but I believe there absolutely is a case for simple assault (if such a charge exists in Thailand) in his aggressive and threatening demeanor toward her and her friend. I think that should be VERY easy to convict him on. Sometimes lawyers go for charges that require a higher bar of evidence and end up losing, when they could have gone for a lower charge and won. That's what this appears to be IMO.
Of course, all of that is assuming no brown envelopes were floating around....