First, Presumably he printed this thing with one of those small home printers.
Second, the significance of 3D printing of firearms is that you can print a receiver (i.e, the regulated part) in your own home and use unregulated parts to complete it.
Third, in addition to the receivers, one can print just about any other small part. This is going to be a big thing in the near future particularly since so many parts these days are plastic. Break a part, just print a new one.
Forth, there is also big market of original and after market gun parts available (just look at ebay) to complete just about any kind of gun.
And which of you guys didn't read the story or watch the video where he shot it a couple hundred times and it works?