So the U.S. cannot say "boo" about how U.S. classified information is handled if the person mishandling that information is not a U.S. citizen?
The notion that the law of a nation applies to persons who are not on the territory of the nation and are not citizens of the nation in question is obnoxious to the concept of national sovereignty. Again, if extraterritorial application of laws to non-citizens is acceptable, the PRC can seek to arrest and/or extradite US citizens who have never been to China for actions taken outside of China. If on the basis of treaties, Australia want to prosecute Assange for mishandling American classified information in violation of
Australian law implementing such treaties, there would be nothing wrong with that. I believe we have such treaties with some countries (I think the UK, possibly all of the 5-Eyes countries now), but the US has no right to apply our laws to non-Americans outside of the US, and the assertion of such a right created the right for other countries to apply their laws to Americans in America.