Oh, so it USED to be a fixed gear, and now it's a freehub.
See here for the difference between freewheel and freehub:
http://www.cyclingnews.com/tech/fix/?id=cogs
Most bikes don't have actual "freewheels" anymore.

So now it can't go backwards when you pedal backwards anymore. So someone just wanted to put a regular wheel on the back, or make their other bike into a fixie using your wheel.