I think that's an interesting point. I'm curious: what is your ammunition availability? You can't 3D print bullets yet, or propellant. Let's say I'm British and I have a 3D printer. I can assemble the actual gun with my 3D printer and a few metal pieces. Maybe I can assemble the casings with my 3D printer too. Let's say I also know how to hand load a cartridge. How easy is it to acquire the primer, propellant, and bullet for even a single loaded cartridge? After all, this weapon was assembled and fired in the US, where it is pretty easy to acquire those things.
Well, I wouldn't say that it's really "caused" by one guy. He may be the first who has done it, but the promise of 3D printing from the beginning has been a brand new way to manufacture things, not a specific class of things such as "things that will not cause societal disruption." Somebody was bound to do this, if only as an engineering challenge. Heck, I'd be pretty shocked if actual firearm manufacturers were not 3D printing their product within the next hundred years.