You're correct, but the issue is this covers the manufacture of RIFs too. I.e. removing the paint. Also, with buying, the liability is on the seller (the shop or person) and not the eventual owner. However, with manufacture the liability is on the person who manufactures it.
With both of the above: There is nothing about ownership. The law governs those few minutes in which the crime is being committed. Unlike owning a section 5 firearm where you're breaking the law just by owning one regardless of where you got it.