Maybe the guy who delivered it did so in the Ace Ventura fashion.
Did the package look like it had been opened then taped back up again? It seems weird that if they knew what was in it, they would just crush/twist them and send them on their way. I would think they would either confiscate them right at customs so they could say they intercepted illicit drugs, or after discovering them re-tape the box and set up a sting.
Doesn't make sense to put a warning sign on the bait you're using to catch a fish. Still seems really off... I gotta admit that it takes some balls to receive clones in the mail. I'll stick with seeds myself.