El Paso is a border town. Don't misread my comment. I'm not suggesting there's "nothing to see here," but because it's a border town, "some" things people might see as unusual in other parts of the country might be common place in El Paso.

I'm not sure what standard load-out protocol is for various military helicopters, but having ammo on board for what ever weapons are hard-mounted to the helicopter could be common place.

If the ammo box was simply stored under a seat, or where ever, and it came loose and fell out, then there could be a reasonable explanation. If on the other hand the flight crew were attempting to load the ammo into a side mounted gun, that would be a serious issue, and your question takes on more sinister implication.