Nothing illegal about selling a long gun to someone across state lines.
I know I can ship to an FFL in TN. This guy wanted to drive down and take the gun back with him in a private sale.
From the ATF website:
"May an unlicensed person acquire a firearm under the GCA in any State?
Generally, a person may only acquire a firearm within the person’s own State. Exceptions include the acquisition pursuant to a lawful bequest, or an over–the–counter acquisition of a rifle or shotgun from a licensee where the transaction is allowed by the purchaser’s State of residence and the licensee’s State of business. A person may borrow or rent a firearm in any State for temporary use for lawful sporting purposes."