Regions like for TV and movies. IE, they sold a drive in Asia and someone sold it to us. We do a warranty check and are told that we can't get a warranty for that drive because we're in the US.

It's worth doing a warranty check with the manufacturer as soon as you receive the drive if there's any possibility at all it might not be up and up, so that you have an opportunity to return the drive if you want to.

Even if the drive is legitimate, a vendor might sell you an OEM drive which means having to go through that vendor for warranty service instead of direct with the manufacturer. That might be too much of a hassle.

Often the drives are sold at different prices in different regions. For instance, I have a few WD Reds (NAS 24/7 grade) cheaper than Blues (consumer grade). They have the words "Not for sale outside Mainland China" in big bold writing on the label. They are usually parallel or grey market goods, in my case they were brought into Hong Kong by parallel traders who probably brought infant formula or medicine back into mainland China

Gray market: The short version is that the exact model that was purchased was intended for a different region due to price segmentation at the manufacturer/brand. The item would be genuine but the manufacturer won't support the item if the customer is outside the intended region.

DVD/BluRay implement a lot of the distribution layer of segmentation in hardware and software, but the notion exists in lots of goods, such as in the marketing of high-end watches to different countries.

I assume they got a drive that wasn't meant for their region of the. When they tried to initiate an RMA with the manufacturer, it appears they wouldn't accept it.