The point is this. The magistrate, who had far more information and experience in these matters than we do, determined that the evidence supplied was insufficient to come to a determination of guilt. The magistrate is apparently unconvinced that what the witnesses saw, was what they determined to be happening. She would have discounted anything more than what they observed, not an interpretation of what they observed which is inadmissible, and that the offender and alleged victim would have a far better idea of what occurred. She can only go on the evidence supplied and she determined that, without disputing what the witnesses saw, they could not have been close enough to make a judgement as to whether he pulled her hair or grabbed her shoulder and accidentally pulled the hair, (quite reasonable if you think about it) and what actually caused her to fall. The police evidence is limited to the phone call. They did not witness the incident and therefore anything they report is based on post observation and what witnesses claim to have seen.
Now what the alleged victim is saying is quite feasible, as is what Walker claimed. The fact that the alleged victim qualified some descriptions of the event later on again is not sufficient evidence to suggest she was covering up for Walker. Changing statements is actually quite frequently done, and does not inherently mean an attempt at deception. Many times victims make statements in the heat of the moment and then on reflection realise what they thought happened was not quite as they reported. Happens a lot. There was insufficient evidence to suggest he had assaulted his partner. Whether he did or didn't only the gods, and the couple involved know for certain. Anything we now say is pure conjecture and that is something we may think, but we have no right to state it publicly. The case has been determined full stop.