Cos he pleaded guilty right from the start so the case did not go to trial. The magistrate could only sentence him based on what's allotted under the act he was charged with, and that too after considering all the mitigating factors (which include saving the court's time)

Had he claimed trial, It will probably take many more months or even years before the case goes to trial and only then can prosecution present its case to the court including the video evidence submitted.

I doubt the judge would go easy on the guy had she been able to get a better picture of what actually transpired.