The other photos are posed as well. The downed wreckage, the Ca Mau operating room in the swamp, the Lam Son 719 photo are well known photos that were staged. You can find similar photos from the Battle of Dien Bien Phu. The French POWs were asked/made to recreate the final battle for photographers.
An Eastern Bloc country, I believe the USSR or East Germany, sent photo equipment and photographers to North Vietnam. They understood the propaganda value of these photos.
And don't get me wrong, these photos are very valuable in reinforcing morale and swaying international opinion. The West does it too. There was less staging of photos by the West back then as they tended to have more people taking photos of the action at the time.
