Then again, a non-citizen can be an enemy combatant!
If he meets these criteria:
Lawful Combatants. A lawful combatant is an individual authorized by governmental authority or the LOAC to engage in hostilities. A lawful combatant may be a member of a regular armed force or an irregular force. In either case, the lawful combatant must be commanded by a person responsible for subordinates; have fixed distinctive emblems recognizable at a distance, such as uniforms; carry arms openly, and conduct his or her combat operations according to the LOAC. The LOAC applies to lawful combatants who engage in the hostilities of armed conflict and provides combatant immunity for their lawful warlike acts during conflict, except for LOAC violations.