Having set aside the discharge, Justice Collins said he would normally substitute the District Court's decision with his own, but Filipo had only pleaded guilty due to the sentence indication that he would be discharged without conviction.
He would allow Filipo to vacate his guilty plea if he wanted to, in which case the matter will be sent back to the District Court for trial.
In Justice Collins opinion, the starting point for sentencing should be two to two and half years' imprisonment.
In the ruling, Justice Collins notes an affidavit from the head of the police prosecution service stating Filipo's victims had notified police that they believed an appeal should be filed because the "factual basis of the sentencing was inaccurate".
The police prosecution service explained that either through an oversight or miscommunication within the police prosecution service, Filipo's case was not referred to the Solicitor-General when it should have been.
Justice Collins allowed the extension of time to apply for leave, despite saying the reasons given for the delay in filing the application were "not particularly satisfactory".
"The desire for finality in criminal proceedings is an important consideration. There appears to have been a delay of approximately 10 months between the date Losi Filipo was charged and when he was discharged without conviction. In the overall context of this case, the 13 day delay by the police prosecution service is comparatively insignificant."
Justice Collins found the sentencing judge "did appear to harbour a degree of uncertainty about the genesis of the assault".
"The source of Judge Davidson's uncertainty appears to have been the statements in Losi Filipo's affidavit . . . In particular, Losi Filipo portrayed his role as being one of assisting his brother after the fighting had started and that he was hit before he delivered any blows. Losi Filipo's explanation about the genesis of the assault conflicted with the agreed summary of facts."
However, Judge Davidson was "obliged" to base his sentence indication only upon the agreed summary of facts and victim impact statements, which named Filipo as the aggressor.
Justice Collins also noted the sentencing judge did not refer to the fact Filipo stomped on the head of one victim.
"Those stomps were particularly serious and occurred when Gregory Morgan was already unconscious. This is the most disturbing aspect of Losi Filipo's behaviour. It was potentially lethal conduct and required specific consideration," Justice Collins said in his notes.
"Judge Davidson appears to have understated the seriousness of Losi Filipo's conduct by not specifically referring to the fact he stomped on Gregory Morgan's head on about four occasions."
He also pointed out Judge Davidson had referred to the assaults against the two female victims as "not particularly serious in themselves" and "more in the nature of pushing and shoving".
Justice Collins said the description "only partially" reflected the agreed summary of facts, which portrayed the assault on one victim as more serious than how Judge Davidson had described.
Crown prosecutor took issue with Judge Davidson's starting point of one and a half years in prison. Justice Collins found a starting point of two years should have been adopted.
"A starting point of two and a half years' imprisonment would be unimpeachable," he said.
"I am satisfied Judge Davidson erred when he overlooked relevant matters relating to the gravity of Losi Filipo's offending."
Those matters were Filipo's role as instigator, the stomping on the head, and the serious consequences for the victims.
Justice Collins also addressed the allegation Judge Davidson overstated the consequences of a conviction on Filipo's career.
He said it was impossible to predict if a young player will evolve into a professional rugby player, and a conviction would not prevent Filipo from obtaining a professional rugby contract, it would only make it "much harder".
"It is the conduct of Losi Filipo and not simply whether or not he is convicted that is the key consideration for rugby administrators and future employers," he said.
Judge Davidson did not have sufficient evidence to conclude a conviction would be a "real and significant barrier" to Filipo fulfilling his ambition to become a professional rugby player, Justice Collins said.
"Judge Davidson therefore erred by taking into account an irrelevant factor . . . this error was also an error of law."
Justice Collins would hold a hearing on November 2 to reach a decision on whether or not the case should be sent back to the District Court of if any sentencing should be dealt with in the High Court.
