Well he claims to be a “tourist” so not dual.
“Is it legal for Americans to serve in foreign militaries?
Yes, they can. According to the US State Department, joining the armed forces of another country (which is not engaged in hostile actions against the United States) does not cause loss of US citizenship unless the person in question does so with an explicit intention to relinquish US citizenship.”
And, from your resource. “Americans contemplating joining the war in Ukraine or already there need to know, however, that they risk violating the Neutrality Act, a foreign relations law dating to the nation’s Founding Era. The criminal liability risk mainly pertains if Americans join Ukraine’s forces within U.S. jurisdiction, or organize and launch a private military expedition against Russia while still within the United States.
Further complications are ambiguous terms in the law’s text, and that the statute has not been consistently enforced over the course of U.S. history. Some experts have predicted that Neutrality Act prosecutions of Americans for fighting for Ukraine are unlikely. Yet the law remains on the books, it has been enforced in recent years, and the Department of Defense last week pointedly urged Americans not to join the fighting. The risk remains that well-intentioned Americans could blunder into committing a crime.”
Kind of negates the header.