Hmmm, now that I read this more completely it's possible that the other customer did indeed receive a new hard drive, not Bruce's -- but it may have been used to ghost Bruce's hard drive before to get the data off it before they sent it to Gateway. That's the quickest way to get the data off the bad hard drive before it completely fails. Then they burned the data from the new hard drive to the DVDs to give back to Bruce, but they neglected to erase the data from the ghosted hard drive before they installed it into the other customer's computer.
So it could indeed have been a new hard drive the customer received -- just one that unfortunately had Bruce's personal data copied onto it. Poor procedure and very sloppy work by possibly multiple technicians if that is the case.