"And that's all perfectly legal, he wasn't doing some black market thing"
Ummm... It's the #2 question in this ATF FAQ
https://www.atf.gov/resource-center/docs/0501-firearms-top-10-qaspdf/downloadTop 10 Frequently Asked Firearms Questions and Answers
2. May I lawfully transfer a firearm to a friend who resides in a different State?
Under Federal law, an unlicensed individual is prohibited from transferring a firearm to an individual
who does not reside in the State where the transferee resides. Generally, for a person to lawfully
transfer a firearm to an unlicensed person who resides out of State, the firearm must be shipped to a
Federal Firearms Licensee (FFL) within the recipient’s State of residence. He or she may then
receive the firearm from the FFL upon completion of an ATF Form 4473 and a NICS background
check. More information can be obtained on the ATF website at
www.atf.gov and
http://www.atf.gov/firearms/faq/unlicensed-persons.html. The GCA provides an exception from this
prohibition for temporary loans or rentals of firearms for lawful sporting purposes. Thus, for
example, a friend visiting you may borrow a firearm from you to go hunting. Another exception is
provided for transfers of firearms to nonresidents to carry out a lawful bequest or acquisition by
intestate succession. This exception would authorize the transfer of a firearm to a nonresident who
inherits a firearm under the will of a decedent. See 18 U.S.C. 922(a)(5).