Is it true that courts have to abide by the judgements made by other courts?

I heard of a recent case in the UK where a 22 year old was arrested for possession of 1 joints worth of cannabis was dismissed in court with an absolute discharge because, as the Magistrate said of his "unusual" decision: "It was a tiny amount." Does this mean effectively that all instances of possession of 1 joints worth of cannabis must now also be given an absolute discharge if taken to court, because of the previous court ruling that possession of a tiny amount of cannabis is not punishable?