Oh I agree. It is very likely that the electronic checks are recorded and could be used as a non-official registry of gun owners. I removed my comment to that effect because it is speculation. But, electronic records are so easily recorded that I have little doubt that the electronic checks are in fact an illegal registry.
Seven states have required gun registries. It is not illegal for a state to have a registry. It is illegal for the federal government to have a gun registry with exceptions for NFA controlled arms.