As far as I know it cannot be. Their end run around the constitution to outlaw arms, was their ability to regulate commerce itself.

By milling your own 80% lower, you are making the gun for yourself. If you do not sell it, it is not involved in commerce. There is one caveat as the guy in the video mentions, he says if you are legally prohibited from owning a firearm, then you cannot do this.

That statement may or may not be propaganda, I am not certain, because as you said they seem to be able to do whatever they want with their laws. Most of it involves their ability to regulate commerce.

If you are interested, feel free to join the information war on discord.
That link should be good for 24 hours. All the best, it's definitely worth researching!

^{P.S. None of this should be construed as legal advice, I am not a lawyer.}