Eh?

It's just a thumb drive, on a lanyard, hanging in a cabinet. It's not like it has guards posted. :)

Maybe Joe (from shipping) took it back to his desk to have a squiz at it and try to passively learn something new during some otherwise-downtime and never returned it -- years ago. That cabinet is in his area, so he has the key.

Maybe Tim (the plant electrician) borrowed it to get something else done, and it unintentionally disappeared somewhere along the way. Tim has all of the keys for all of the things.

Maybe Emily (the ubergeek who prides herself on being able to code her way out of a mess on any system) had it in her office before she got hit by a car and lost the ability to communicate with polysyllabic words. She borrowed Joe's cabinet key after he mentioned an issue.

Either way, it was just a thumb drive that had been inside of the cabinet, and now it is gone.