All able-bodied Vietnamese men were to be in the military so I bet this man was not a “friendly” Vietnamese. There were few symbols or uniforms to identify friend from enemy and that made everyone an enemy until they proved to be a friend. Men, women, children and even an ox were suspect. Men were most suspect and someone should have checked this guy. However stopping a convoy to check one man could have triggered a trap and at a minimum would be a tactical error.