A key input into the bit of the judge's decision that people are calling out, was that some of the changes effected by the amendment to the Sex Discrimination Act in 2013 that added in gender identity as a proscribed ground of discrimination deliberately muddied the meaning of "sex" at law:
ParlInfo - Sex Discrimination Amendment (Sexual Orientation, Gender Identity and Intersex Status) Bill 2013 (aph.gov.au)
The definitions of man= male and woman=female were taken out deliberately:
Per the EM "These items will repeal the definitions of ‘man’ and ‘woman’ from subsection 4(1). To the extent these terms appear in the Act, they will take their ordinary meaning. These definitions are repealed in order to ensure that ‘man’ and ‘woman’ are not interpreted so narrowly as to exclude, for example, a transgender woman from accessing protections from discrimination on the basis of other attributes contained in the SDA."
Ironically the next paragraph refers to males and females: "It is not intended that by repealing these definitions the SDA would be limited in its application to only adult persons, but that ‘man/men’ and ‘woman/women’ continue to refer to all males and females respectively." (presumably what they meant to say was that it was intended to continue to refer to men and women of all ages?
It also says "The definition recognises that being intersex is a biological condition, not a gender identity. It does not require a person who is intersex to identify as either male or female in order to access protections under the SDA. The definition is not intended to create a third sex in any sense. It does, however, recognise that sex is not a binary concept and that an intersex person may have the biological attributes of both sexes, or lack some of the biological attributes considered necessary to be defined as one or other sex."
The key problem for Giggle is that they were seeking to defend a case of "sex" discrimination on the basis that Tickle was a man (and then they could rely on a provision permitting sex discrimination for good purposes); legally he was a woman and he wasn't alleging sex discrimination, he was alleging gender identity discrimination.
It seems to me that the judge may not have been personally invested in the outcome that legal logic led him to. He makes it clear at the start that while the Giggle side are challenging both the validity and legitimacy of self-ID and its consequences, he only has the ability to rule on validity issues. As he quite rightly says, "Any debate around the concept of woman, of womanhood, or gender more broadly as a natural, biological, or social construct falls well outside what I must, legally, determine in this case."
He's bound with an interpretation of the legislation that is consistent with its purposes and with relevant case law.
Maybe an appeal to address the incredible breadth of the external affairs power in the constitution - I'm told it all went wrong with the Tasmanian Dam case back in the day.