The burden of proof is to establish "guilt" without any reasonable doubt. Evidently, the judges considered there was a reasonable doubt, so Pell is considered to be innocent as we all are. However, whether in reality Pell is "innocent" we do not know because the result simply says that there is some doubt as to his guilt, thus they cannot convict him of the crime.
If many people see this as a travesty of justice then too bad. This is the way the law works and requires a very high standard of proof before anyone can be considered to be guilty of a crime.
