We opened up the case of a USB stick (that didn't work before we opened it) and it looks like this:
Has the memory been taken out of it or do some USB sticks actually look like this? Note that it was probably cheaply-produced.
Well the pictures aren't 100% clear but it could be that all the electronics fit inside the USB plug.
If the drive works ok in your computer this is the case.
If you are adventurous you could try to open the metal casing of the USB plug. Warning this could destroy your drive (so backup data first).
One would actually have to check both halves of the caseing, but just from looking at the picture this half of the case does not appear to be designed to hold more than it currently does.
As such it at least appears unlikely that something has been taken out.
If the person had their work on it it is probably a real USB.