Hi,
There is a big difference between muzzle down and dragging the muzzle in the mud. A muzzle down by a security person is on dry flooring/pavement/concrete, and it NEVER hits the ground.
Notice the angle he is carrying it. It is behind him. That would destroy the forward site. If the muzzle hits the ground, it gets filled with mud and the next time he fires the weapon it will explode in his face.
Muzzle up Muzzle down, no matter, but I never saw anyone hold their rifle by one hand and that hand on the trigger handle. It doesn't make any sense to hold that way. For purposes of credibility I spent 1 year in Vietnam, mainly as a platoon leader.
If only he would dip it in the mud.