It goes straight to a CPC official's goon cave

Where it says returned it means if it's being imported commercially. For example you order such materials by paying and some company ships them to you directly, they get stopped, customs may exercise the option to order them returned to sender via whatever courier they were being sent by. For individuals they're not going to hold your stuff for you and bother making sure it gets back to you, it gets destroyed. More than likely such a provision mainly applies to other prohibited goods, say good faith attempt at importation of something for commercial purposes which is technically prohibited but valuable may be sent back rather than destroyed.

so in theory they might send it back, but every single news article about this indicates that they get destroyed, so that seems to be the "in practice" reality.

I've only had stuff seized in Australia but when you think about how many thousands of people transit through each customs checkpoint daily (and how many people just bring stuff without really thinking about it at all) it would be a huge logistical challenge to track and return things. As I understand it, at the time I could have taken a receipt and paid a lot to try and get the things released but they were blatantly illegal so I was never keeping them. For the most part everything that isn't significant enough to result in fines or criminal charges just goes in a big bin off to the incinerators.

I suppose it would also be just ethically/morally/legally inconsistent for the government to ban something but also facilitate its distribution as you depart. So yea I doubt this happens in practice except at large commercial scale.