when you extract a geometry, you make an exact copy of the selected faces, the tutorial tells you to do that and flatten out the extracted copy and work on its UV and then transfer it back to the original source, so i think you gotta select the same exact faces again. thats why you save it as a selection earlier on. the tutorial seems simple enough, if anything you should try doing it on a simpler object, lets say a 32 polygon rock. cheers and dont give up!