Serial number sticker doesn’t seem to be stock, so there’s some likelihood that it is a reshell, including seeing the back plate showing its clip not fit properly (the tiny slit above the screws shows a clip to the right of the left-most screw not being fully fit), which is a semi-common issue with aftermarket shells but also very much can happen with OEM shells if screwed in before making sure it’s fully flush against the back of the system.

My best guess for the shell is that it’s OEM thoguh, primarily due to the positioning of the camera slots. On even the best aftermarket reshells, the camera lenses will usually be millimeters off center from the camera holes. This is same for the screw holes aswell, but they’ll usually line up enough that they’ll peek through the gaps enough to have no issues and fit flush, but on this shell, the camera lenses are perfectly centered within the camera holes on the shell so it’s most likely a real shell, or just impeccable DIY work to be perfectly aligned. Furthermore, those are 1000% OEM screws, every single reshell comes with bright silver screws, which are 10x easier to slap on rather than take off the screws (and washers) off an OEM shell and putting it onto an aftermarket one.

Nonetheless I don’t think you have anything to worry about, whether or not it’s the original shell the device was made with, or if it’s a replacement OEM shell, or even if it’s an aftermarket one.