UPS is effectively acting like a CDN here. Stocking up on COVID tests right at the edge (your local USPS distribution store) and shipping it off immediately when ordered. Hmmm interesting...
If someone is more familiar with a CDN that the traditional retail logistics and distributions infrastructure, then it would probably be more helpful of them to think of the situation using that analogy.
USPS is acting both like a retailer, and as a sort of an analogue to a CDN. Both can be helpful models in understanding how this works.