MYSTERY PART
The dimensions of this part are just about identical to the original IPOD.
If this were a back plate to an aerospace or medical electronics device, then the opening might be for inserting batteries, and a similar latch plate might be made of liquid metal to close it up.
Or, if it were the front, then the opening might be for a screen of the device.
You didn't fully describe the depth dimension or whether it had side cavities for switches or USB ports or something like that.
Is it just a flat plate, or is there some curved edge from the top down to make a noticeable side that you were not able to present in a side view?