The GFSZ act is misguided and counterproductive as this case highlights.
Misguided is much to kind.
My assumption is it was designed to make most carry of firearms for self defense illegal.
That is its major effect. The federal prosecutors have been tip-toeing around it, realizing there is a very good chance it will be overturned with the current US Supreme Court.
The Biden administration has been so anti-Second Amendment, they don't care, which is why we have two test cases.
There is another test case in the Fifth Circuit.