:The Lacey Act is in reference to shipments through USPS.
Exactly where did you see this explanation? I've read the act, and dealt with it through the NYS DEC regarding timber rattlesnakes that come into the state, and it was explained to me that the law is in regard to any violation of a state law(in this case possessing a threatened species without permit). Without going into detail, it had nothing to do with how the animals got here, but the fact that timber rattlesnakes cannot be shipped into NY State without proper permits.
I'd be interested in seeing the info you found explaining that it only applies to USPS.