I think what skibeagle is getting at, quite correctly, is that they could have had one of their brake units deactivated. In this case, procedures will vary slightly, but in general the wheel in question won't be braked on gear retraction as it normally would be. So you leave them down for a bit (2 minutes if memory serves) to allow the wheel to slow down a bit before you retract the gear, as described above by Joe.
Cheers all