What reallly happens at the end of the movie BURIED?

at the end of the movie as Paul is about to be rescued the man on the phone says "im so srry... you lead us to mark." earlier on the film the very same guy trying to rescue him tells him that he has saved a man named Mark white. i know the man did it on purpose so Paul can have a sense of hope, but WHAT I DONT GET is how he lead them to Mark. i mean how did that happen... how did he lead the rescueres to a wrong place. ( also there is this theory that the rescuers actually do find paul but look at the other side of the casket and thought "wait mark white was here." by the time he can respond to this remark, his head is BURIED inside the sand:(( ) im not convinced with that possible ending... soooo what do yoouuuu think??:))