I don’t know. I think this is sort of a slippery slope. On the one hand, yeah it makes sense. On the other why don’t they go even farther? It becomes a rabbit hole that is very deep, and in many cases highly subjective.
I think given that the laptops are coming from Purism themselves, and then given to a carrier (UPS, USPS, FedEx), the integrity of your box is subject to the carrier. You can assume there are no security problems coming from Purism (otherwise, why did you order from them?).
Depending on where you live, there are many possible vectors of problems that are completely outside of Purism’s control. So if you are truly paranoid about all of this, then you have all the tools to ensure you are secure.