Again, in the context of the photo, which is a Military Inspection, the rifle is not field stripped. The rifle is emptied of all ammunition, bolt is locked to rear, the breech double checked, and the barrel is checked through the muzzle which is the only way for that particular rifle. Given the checks and state of the rifle during the inspection, it is a perfectly safe method of performing that check.
You can further field strip the rifle, but this is done for cleaning and maintenance. It is not necessary for an inspection, nor is it expedient to do so. It is still safe.
Look at this
site for a picture of a shotgun that breaks. That is what is meant. You can see from the breech to the muzzle. An AR15/M16 can also do this by removing the rear receiver pin, "breaking" the rifle and removing the bolt carrier group. They are not "break actions", but they can simulate it. You have a direct line of sight from the breech to the muzzle. Bolt actions can also give you a direct line of sight by removing the bolt.
None of this trivializes the "muzzle in a safe direction" rule. It is a good rule to follow, and it is still maintained in the military. However, when performing inspections, the rifle is cleared in such a way that there is no doubt it is empty and not able to readily fire when it is placed into the hands of the inspecting officer. It is safe.
One last time, to reiterate, the rifle in the photo is an M1 Garand. You have to look through the muzzle to check the barrel for cleanliness, which is the purpose of the inspection. The steps employed in clearing the rifle before handing it off the to the inspecting officer are no less safe than field stripping it. The rifle is still empty.
Also, the barrel of an AR does not come off easily.