Put it this way. I would trust the packaging over someone's word that they opened the packaging and tested it. I would trust it 10x more if I bought from the manufacturer's site.
Despite their good reputation (mostly associated with their RAM), Kingston is just a repackager of third-party parts. They don't actually make any of their products themselves.
Therefore, you indeed can't trust their original packaging if they themselves don't vet their supply chain properly.
This is in stark contrast to manufacturer-vendors like Samsung, Micron (Crucial), and SanDisk (Western Digital) who manufacture either all or at least the core components of their products and have their own manufacturing reputation on the line.
OK well, there may be exceptions. But surely you accept that most manufacturers are more reliable as a source than most resellers, don't you?
If you have to be 100% sure then there is no substitute for doing your own tests. But the context here is trying to avoid that either by paying someone to test for you, or by using a trusted source like some actual manufacturer.
[0]: https://www.bunniestudios.com/blog/on-microsd-problems/