The latin version of the name Gyula is Julius, so that would be correct oh his Australian passport. Sopron and Odenburg are the same place. Sopron is the Hungarian name and Odenburg the german name for the town. It's right near the Austrian border, so the name reflected who controlled the area.
He is wearing a wehrmacht army uniform, without his records its impossible to say what unit he was in. He could have been in one of the service battalions recruited from the Hungarian ethnic Germans. Does he list a unit or service number in his papers? Maybe a postmark from a military postal unit?
Over 200,000 ethnic Germans were expelled from Hungary at the end of World War 2. That could easily explain his being in a displaced person camp, at Kufstein in the American Zone of occupied Austria. Most ethnic germans who wound up in the Soviet Zone never escaped. Many ethnic Germans immigrated to Australia.
He may have been a prisoner of war for a time before he was sent to the dp camp, you can check with the Red Cross to see if they may have any information-https://www.icrc.org/en/document/request-information-about-i...