There is a 3rd possibility: sellers are completing the product page with incorrect metadata. This might even be down to simple user error eg someone non-technical given the data entry job.

I'm not saying Amazon isn't full of dark patterns and other problems but if there is one thing I've noticed on nearly every online store since the dawn of online shopping, it's that there is always the odd product that has been incorrectly classified. This problem only becomes magnified when you allow 3rd parties to complete product pages.

For me though, the most annoying anti-pattern goes to eBay and how it will bulk out it's results with items from other countries even when you specifically state a local region.