The point in religion is whether X is essential for the operation of that religion to benefit from relevant human rights. In that case, X was a purity ring so the court had to decide whether a purity ring was essential for the religion to operate. The religion concerned was Christianity, and a purity ring was not any part of traditional or customary Christianity rather the purity ring is a modern use by certain churches, ie the Born Again' movements, not shared by the churches in general. Alternatively, a purity ring is not essential for the Christian religion, neither is a cross for that matter. Human rights are important, but these rights are based on essential things.
In any event, freedom religion is not a right as such it more a privilege as the state has qualified right to interrupt any convention rights including religion in certain circumstances. The school raised the argument about jewellery but this is a side issue.