Californians may ship a gun directly to the manufacturer or to another FFL holding gunsmith, and take direct delivery of that gun on return.
If a dealer ships the gun to the manufacturer on behalf of the owner, then it depends whether the dealer enters the gun into their inventory before shipping in order to transfer the gun to the manufacturer rather than just shipping.
The complexity of California gun law is onerous enough by itself. Sadly, it is often compounded but the (cough) legal acumen of various sharp minds in the firearms business. We are subject not only to the law, but a particular dealer's interpretation. I expect many retailers are unfamiliar with the details of the law in this area and just do what they do for any other delivery.
On this forum, we have almost all seen the common misinterpretations of statute around antique firearm status. Californians are constantly burdened with similar thoughts from the sharp legal minds behind the counter at the gun shop. I have, more than once, been asked to do a 4473 on an antique gun, by a dealer who knows no better. All we can do is decide whether to acquiesce or refuse.
I have no idea why I felt compelled to editorialize on this particular subject this morning, but there you have it