The individual you might be referencing could be someone like William Joseph (Bill) Hales, who was an Australian that fought for Germany during World War I. There were indeed cases of Australians of German descent who served in the German military during the war, particularly due to familial ties or personal beliefs.
It's important to note that many Australians with German heritage faced significant discrimination and hostility during and after the war due to anti-German sentiment. If you had a specific person in mind or more details about their life or background, feel free to provide them for a more focused discussion.