Don’t need a CNC. All you need is a decent drill press, router and a work bench. You can buy the 80% complete receivers and jigs from damn near anyone these days for a pittance. A good day in the shop and you’ve got yourself a lower ready to finish out. And no one is the wiser.
I think the original point was that if you couldn’t buy a receiver, 80% or otherwise, a CNC would do.