Saying that Oratory has "won" is too simplistic. They have won a partial victory. They objected to the Adjudicator's findings on 10 points. They won on 5 points with a partial win on another point.
I find parts of the judge's decision (which can be read in full here) surprising.
The judge said that it is ok for the school to request parents' baptismal certificates as proof of their faith and that this does not breach the Admissions Code. However, paragraph 2.5 of the Code prohibits the school from asking for any evidence that would include personal details such as maiden names. Since the mother's baptismal certificate will include her maiden name this would appear to be a breach of the Code. The judge basically says that if the school sets admission criteria that are otherwise legal and where compliance can only be demonstrated by producing a document including the prohibited information they can request that document. I think the judge is wrong on this point.
I do not understand how the judge concluded that it is permissible for the school to include an oversubscription criterion based on previous attendance at a Catholic school. The Admissions Code paragraph 1.9b is clear that only named feeder schools can be considered. I have read the judge's reasoning on this point and I find it illogical. He says the school's approach makes a mockery of the feeder schools provision in the Admissions Code but upholds it anyway. He suggests that "taking into account previous schools attended", which is prohibited by the Admissions Code, only prevents the school taking into account specific schools but does not prevent them taking into account an entire class of schools (i.e. Catholic schools). With respect I believe his reasoning on this point is flawed and hence his conclusion is wrong.
Some other parts of the decision are less surprising. The Adjudicator decided that "having regard to diocesan guidance" meant the school must follow it unless there was a compelling reason not to. I believe the judge is correct that this was too high a bar and that a clear and proper reason was sufficient.