Based on package labeling I would say this is NOS. It wouldn't surprise me if someone had a box of these that was surplused.
You can just ask Pasternack. Their reputation is top-notch and they supposedly have 24/7 global support. I
would be shocked to find these 'surplused', as they are a completely current product and quite marketable. Stolen perhaps, but I still doubt we'd see them at these prices or that yours would have blown up.
Also consider that these have obviously already been cloned as replica versions that don't claim to be Pasternack and they appear all over eBay. So the shell and hardware are already available, all you have to do to make a fake is add some markings and a package. The only mystery is why they are being so obvious and selling them as new. They're worth more in used condition.
https://www.ebay.com/itm/274310407299https://www.ebay.com/itm/174741192533This could be a supply-chain security issue as well. The Pasternack version is purportedly assembled and tested right here in California, but if the shell and connectors are subbed out to a Chinese contractor and the final product is assembled here using an expensive attenuator element, well you can guess what happens next.
Based on your tests and the fact that 12.5W will fry it, what you have may actually be an attenuator only good for 3GHz and thus you simply toasted it by actually exceeding 10W.