Well, it's like any other law - if a cop or ranger wants to nail you for something and you're breaking a regulation such as this, they can get you. I'm not agreeing with it, it's selective enforcement from a ranger who probably doesn't like the border groups, but if the border groups go onto National Park lands, they will be subject to this, so they should avoid doing such and IMO stay on private property where no one can legally touch them.
In addition to the legal firearm, legal two-way radios, and legal scanner, his legal camera was seized. This camera is the same camera he uses as a tool of his business as he is the editor and a reporter for the Tombstone Tumbleweed newspaper.
Also, not reported, was that the female park service officer that stopped these hikers held a gun on them. I'm trying to get confirmation from Simcox himself, but apparently the female agent was of hispanic descent and she stated to the hikers that she "doesn't agree with what [they're] doing."
Simcox himself does not know under what specific statute he was given a citation. He doesn't know - no one has told him - what law he supposedly broke.