Return address is the...post office?

Ok so someone bought the Xbox WiFi Adapter that I posted on Amazon (that was a rant in itself..the thing only works with factory xbox and you have to use a disk that only reads on a factory xbox to get the adapter configured). Anyway...I put my return address on it and the recipient in the USPS click and ship. I go to the post office in Alpha, Ohio (essentially Beavercreek) and the lady goes "if you used our zip code we'd get credit for shipping it". Now...am I just being ridiculously misinterpreting or does that totally NOT make sense? I mean, the recipient should have a proper return address on the package. I'm not going to lie. That zip code is not MY zip code nor a Xenia zip code. It would be like putting the post office as the return address which makes 0 sense. Who looks at the shipping from zip code at the post office? I've never had anyone beg for zip code "credit". How odd.