His former partner also said he had engaged in stalking and threatening behaviour after their six-month relationship ended.
After initially denying the charges, Mr Witehira pleaded guilty to one charge of assault with a weapon and one of reckless driving.
There was no real prospect of imprisonment, in the court's view, but Mr Witehira was led to believe that there was and that he rushed into changing his plea to one of guilty out of fear of going to prison.
The court held that Mr Witehira's guilty pleas were entered without a proper understanding of whether imprisonment was ever a prospect in the event of a conviction.
The Court of Appeal determined that the guilty pleas should be vacated and the convictions quashed.