According to the write-up, the ATF didn't have a warrant for the kit. They "requested" he turn it over, and they threatened to return "with a warrant" to "raid" his home to find it.
Why does that sound fishy? The ATF should arrive with a warrant to confiscate the kit FIRST. No warrant == no confiscation.
If they return with a warrant, and the owner turns it over, there is no justification for any "raid."
Sounds like a heavy-handed tactic to avoid getting a warrant. More than likely because the owner broke no laws. Therefore, there is no probable cause for a warrant.
If it were me, I'd say, "Get a warrant." If they can, they will. I don't think they can -- legally.