Close but not quite.
At question is some polymer lowers from
EP Armory. As you can see in addition to little pins that stick out for the holes they have a molded insert for the fire control pocket. The ATF has stated (with no evidence) that EP molds the lower, then fills the Fire control pocket with that little white plug. That means there is a time during manufacture that the fire control pocket is open and at that point, presto, it's an unserialized firearm. Ares is a major reseller of EP Lowers and so the ATF wants their customer list to track down the firearms.
The problem is that that ISN'T how the lowers are made. That white plug is placed in the mold and the lower is formed AROUND it. At no time during the manufacture of EP lowers (according to EP) are any of the five steps the ATF has held to be "finishing" completed. So they don't have a case, there are no unserialized lowers and Ares doesn't want to give out their customer records.
Personally I bought some swag from Ares when I read about this, and sent them an e-mail explaining why. I'll shoot them some more business when I start my next project.
I suspect that the ATF didn't realize how big the "make your own" firearm hobby had gotten, and with Sen. Ghost Gun spouting off, they are trying to DO SOMETHING (tm). Being in CA only makes it easier.
ETA: That page I linked has a video of a guy completing one in under an hour with a dremel, and a drill. They might be wound up about that as well. The polymer 80% lower thing is going to make a LOT more folks think about building a gun, just because it's so much easier and cheaper. Completely unrelated I got my shipping notice for my Polymer80 lower this week.