This is false. The related case would have left machine-gun building a matter of State law. Pure-Federalism is not the only possible form of governance, and it's not the US Constitution's approved form.
We were talking about federal laws and courts. I assume that in a short blog post I'm not expected to address the proliferation of overlapping jursidictional priorities and conflicts. But since you insist on taking the discussion where it wasn't going...
Fact is, majority of US states do permit machinegun ownership, so long as it complies with federal law; thus if federal law permits felons building machineguns (so long as it remains in-state), majority of states would not prohibit it. Now that the discussion has clarified that the remaining prohibitions would occur in a minority of more than four dozen states, and that the federal government would have at least had no say in the matter (as opposed to compulsive legalization in all encompassed jurisdictions), and that the discussion had not been addressing state laws (or if it did, it was that the applicable state ALLOWED the activity), that for most practical purposes the one-sentence summary of the horribly verbose & convoluted verdict in question and its consequences was sufficiently accurate?
(Pardon me. I'm getting increasingly irritated by exchanges that amount to: "X." "X? You're WRONG because you didn't address minor tangential issues Y, Z, P, D, and Q in comprehensive detail, all of which had little to do with the discussion at hand.")
Oh, it goes much, much farther than that.
The US Supreme Court has ruled (see Raich) that the federal government is justified in sending an armed raid into a terminally ill old lady's home because she allegedly was growing six marijuana plants under her doctor's supervision & approval for her sole personal use in accordance with state law. The "justified" rationale? Her home-grown state-legal personal-use herbs decreased demand in illegal inter-state commerce, therefor affected inter-state commerce, therefor was subject to federal regulation. I kid you not.
(Consequential tangent: if the court had not ruled that way, a pending related case (Stewart) would have permitted felons to home-build their own machine-guns. The court was faced with bizarre rulings whichever way they went with Raich.)