Nothing you said is incorrect.
However, I’m interested in the background. Is this just a simple case of “felon in illegal possession of weapon”, or is it “felon in illegal possession of NFA Class III weapon”.
If it’s the latter, starts to fall into the “Black Swan” category”. How did he pay for it if it was going for anywhere near the full market value? If he didn’t pay full market value, what else did he do to acquire it? How many more of them are there out there?
There are illegally made full auto weapons out there. I seriously doubt this clown had one. But they do exist. Clever people can convert the semi auto ones to full auto.
Back in the early eighties and the seventies, you could mail order parts to convert practically anything into full auto. There are still some of those parts floating around, and there are people with enough skill to duplicate these parts in their garage.