A “lower” for things like an AR15 is an unfinished hunk of metal that you need a drill press etc to turn into a gun. Because it was just a hunk of metal when you bought it, it doesn’t have anything identifying to tie back to you and you don’t need to buy it through a Federal Firearm License holder. This law would regulate those “lowers” as far as I can tell, however there’s already millions of them out there at this point.