Funny they didn't mention trying a hooked chert flake of the sort one would use to gut a deer... it would first push in the sheet metal before cutting through it- making the edge bend- and would likely also resemble metal fatigue. Some of the copper artifacts don't have straight edges but rather intricate curves that would seem unlikely for simple bending back and forth motions. There's a copper box turtle shell from the nearby Mitchell site which looks a bit complicated for metal fatigue, though I haven't seen it in person, just photos. The people at Cahokia made copper covered wood ear spools, and used copper to cover the butt end of a sharktooth and chert sword, among other things. For the most part it appeared too valuable to use for everyday items like arrowheads and to my knowledge no copper arrowhead has been found, though there is an abundance of chert, antler, and some bone points. Some related groups -I think at Spiro in OK- made copper axe heads, hafted in wood handles shaped like woodpeckers' heads with open mouths. I don't think there was use wear on any of them. There are also "birdman" plates of copper shaped like men wearing falcon-like capes.
Still other artifacts, from earlier cultures like the Hopewell, had symmetrical holes cut in the copper and could not have been made by bending the metal back and forth. One that comes to mind is a serpent's head knife or spear point. I do recall seeing "rivetted" peices- overlaped plates wth flared copper pins through them that looked like repair jobs.
I think the reporter just grazed the fringes and didn't dwell much on detail.
There's a pretty good coffee table book called "Hero, Hawk and Open Hand" which has photos of some really remarkable artifacts from American prehistory.