I am only a graduate of the Dennis Denuto school of law, but after reading
the ruling and seeing the way the High Court dealt with the cases of Waters, Joyce and Nash, I think Frydenberg is in a spot of bother. The issue appears to be if Hungary automatically conferred citizenship upon his mother and therefore himself. If so, then I think he might be out. While Joyce and Nash were found to be NZ/UK citizens from birth, Waters did have her Canadian citizenship conferred retroactively (albeit a mere week after her birth). All three lost. Xenophon would also have lost having held British Overseas Citizenship since birth except that due to the lack of typical citizenship rights associated with BOC, such as right of abode in the UK, he wasn't considered a dual citizenship under s44i.
One thing that is clear from the recent ruling is that the HC will not accept any form of ignorance as an excuse.