Technology

Neither the gun nor the switch is 3d printed in that video.

But to answer your question, you can make a firearm from actual trash if you're sufficiently motivated. Look at the different guns Abe's assassin made from a couple of years ago, he even made his own ammunition because of it's lack of availability in Japan. Is the point of gun control as it currently stands to limit access to firearms period or to limit their access to good and more easily available weapons? I would say it is realistically the latter, though crossbows and air rifles are completely legal for people who are barred from owning firearms to obtain and use which sort of invalidates that too.