"In-theater military target" is a lazy set of adjectives and nouns for addressing this situation.

The "theater" in the Global War on Terror is the entire globe. The United States is not at war with Yemen.

Abdulrahman was not even alleged to have engaged in "military" conduct, merely being a propagandist.

He was not a "target", he was collateral damage of a strike on someone else.

This is not a heated battlefield death. The nature of war is shifting and using aggressive global militarism as an excuse to handwave around the denied due process of a 16 year old US citizen is disturbing.