Hiya Ronnie, it could have been an argument about the matter of intention and that is what the prosecution would have had to have proved, and it appears that it wasn't.
There is a difference between something that occurs spur of the moment, and something that occurs as a result of thinking abut it and then doing it. This difference has ramifications as to the extent/depth of charges that can be brought before the court.
In my experience, the sentence delivered seems to reflect the weight given by the magistrate to the level of suffered harassment offered in defence, and a lack of proven intent to cause a grievous injury.
I mentioned BWS - the psychological impairment inflected in either scenario is similar, IMO, hence the analogy.