I am presently stationed at Marine Corps Air Station Yuma AZ, which is where the NG responsible for the Yuma Sector are currently based. I have the opportunity to talk to these guys all the time. They use our Armory to store their weapons. One Sgt First Class told me most of their OP's are manned by unarmed Soldiers because their ROE's do not allow them to confront anyone crossing the border. They are to monitor and report only. OP 's manned by an officer or SNCO may have a weapon, as well as vehicle patrols. But once again the ROE makes those weapons useless. These guys have their hands tied behind their backs. When they call the Border Patrol, response time averages 15-20 minutes. What's wrong with this picture? What is gonna happen when one of these soldiers gets killed because the rules have hamstrung him? Will people wake up?
Well, since the "invading army" fired no shots, took no prisoners, damaged nothing, and left, I fail to see what benefit additional "weapons" could have had. And if the NG troops had opened fire instead of doing what they did, it would have been an international incident.
You don't just shoot people for walking into your country illegally. Well, the Soviet Union used to do that, as well as shooting people on the way out of their country (like the BP agents did). But most countries frown on shooting people just for crossing country boundaries.