Except that the statement quoted is incorrect. You can but most of the parts needed to make a gun, but the receiver is legally a "firearm" and you can't buy a completed receiver except by going through an FFL just as you would for a complete firearm.
You can buy unfinished receivers, but generally those require machining -- at least for handguns. I'm only familiar with 1911s -- I'm sure there must be unfinished Glock receivers, how much work is needed to complete those?
But the gun was a .45, and apparently only held six or seven rounds. My initial thought was "1911," but it seemed unlikely (not impossible) that a fifteen year old kid would have built a 1911 "ghost gun." And then there's this, from the MSN link:
According to the instructions you are supposed to complete a Polymer 80 Glock in a mill or drill press. I did mine in a mini-mill. With some care you could do it with a drill and a Dremel.
You have to drill two holes in the frame, cut out two small square sections of the "slide rails" where the steel insert sits for the slide to ride on, and make a (I think) 3/8" radius cut in the dust cover area for the spring/guide rod assembly to sit in. IMO this is where it goes bad, because if you take too much the guide rod can slip down and lock up the slide, and if you don't take enough the guide rod won't sit low enough for the barrel to tilt and the pistol won't function.
Regardless, it's not super complicated, and the kits come with pretty clear instructions, and the bits needed.
A 80% 1911 either needs machine tools, or several hundred dollars worth of special cutters and jigs. You need to drill the hammer and sear pin holes in the right place, cut the barrel seat with a ball nose cutter, and cut the slide rails. The rails need to be reasonably close to straight and parallel. And obviously, unlike the Glock you are cutting all of that in steel or aluminum, rather than plastic.
Neither pistol is a particularly complicated machine for anyone with some machine tool and fabrication experience.
ETA: For added pearl clutching, you can actually buy the steel parts, and
3d print the required polymer parts of a Glock.