Its a suppressor core.
No doubt, this is true. It is a core. But is that the entirety of the inquiry under the law? I'm not so sure (see my post above). Much like a chore boy scrubbing pad, it is also something else. That may be legally significant.
We all should take care not to confuse the ATF's past positions with the law. Since no one wants to risk testing the waters, the ATF gets away with quite a bit without judicial scrutiny. Hopefully this case (and others like it) will mark the beginning of the end of the ATF's overly aggressive positions (i.e., chore boy scrubbing pads, shoelaces, etc.).