You're right, except that information could very well lead to exactly what his citizenship status is.
Probably not. As I cited in a previous post to another person, it is extremely difficult to lose one's citizenship status. Irrespective of what you do, you must do "it" with the intent of expatriating yourself to actually be viewed as expatriating yourself.
See Post #66 for the relevant cites, and pay particular attentions to the following paragraphs at 8 USC...
"...A person who is a national of the United States whether by birth or naturalization, shall lose his nationality by voluntarily performing any of the following acts with the intention of relinquishing United States nationality..."
Thousands of American Jews who enjoy dual-US/Israeli citizenship actually have been members of the Israeli army and HAVE NOT lost their US citizenship. Why, because they didn't intend to forsake their US citizenship and that's the legal standard - intent.
And, there is a Supreme Court case that held fighting for Japan during WWII against the US didn't automatically forfeit American citizenship, if that citizenship was obtained at birth.
More information can be found at...
Advice about Possible Loss of U.S. Citizenship and Dual Nationality
..but, the relevnat section is this...
The premise that a person intends to retain U.S. citizenship is not applicable when the individual:formally renounces U.S. citizenship before a consular officer;
serves in the armed forces of a foreign state engaged in hostilities with the United States;
takes a policy level position in a foreign state; is convicted of treason; or
performs an act made potentially expatriating by statute accompanied by conduct which is so inconsistent with retention of U.S. citizenship that it compels a conclusion that the individual intended to relinquish U.S. citizenship. (Such cases are very rare.)
It's very, very hard to lose your citizenship unless you want to lose your citizenship.