Recently I purchased a 500GB Xbox 360 Hard Drive second hand, and it is in the correct Xbox 360 plastic casing but it has "Made InChina" written on the white serial number part of the back instead of "Made In China" so I wonder if it is a misprint or an indication that the hard drive could be a fake. Other than that little misprint everything else shows as it should.
It's probably user made, the 500gb drives were only ever sold towards the end of the 360's life in 2014 for the S and E consoles. However its been possible to make 500gb drives compatible with any 360 for longer than you have been able to buy them: Hack a 250gb, 320gb or 500gb Sata harddrive to work in the Xbox 360 and Xbox 360 Slim The easiest way to be 100% sure is to open the enclosure, if its a Western Digital drive then it will be user made. Regardless it doesn't really affect anything, the Western Digital hard drives that can be hacked are generally reliable hard drives.
I used a hard drive error test program on my computer and it said the hard drive is a Seagate Samsung Spinout drive
Here are photos, one is of the barcode sticker I previously mentioned and the other shows a little information about the drive as I don't want the remove the hard drive from the casing because I would never be able to get it back together
Humm could be legit then as the hacked 500gb drives you can make with the security sector here identify as a Hitachi drive: Other then opening it i can't think of a way to be 100% sure however.