He's talking about a non over the counter transfer. It's intended for those who live in remote areas with no nearby FFL/SOT. While the CLEO doesn't "sign off" on the Form 4, the nonOTC procedure involves the buyer filling out the 4473, getting it notarized, then sending the buyers Form 4473 to his CLEO and receiving it back. If it happens inside of two weeks you have a fast CLEO and excellent service from USPS.
Silencer Central loves to brag about their awesome "we can ship to your doorstep" and people often think that's so cool, not knowing the ramifications. So does Capitol Armory and others.
Any FFL/SOT in your state can do a nonOTC transaction, but few do because it adds time to getting the silencer into the customers hands. It also relies on the local CLEO doing his part. And the process for the FFL/SOT is a bit different than a normal OTC transaction.
Silencer Central acts like they invented it, but Silencer Shop did it in Texas over a decade ago when they were a retailer.
Here's the ATF Procedure
https://www.atf.gov/rules-and-regulations/docs/ruling/atf-proc-2020-1-–-recordkeeping-procedure-non-over-counter-firearm/download