That is a limited slip rear end in yours. not a locker. The latest version I think...a 2012 maybe 2011 has a locker that kicks in once the rear starts to slip.
That video is on Youtube as well and I swear I hear the guy say that he is locking it in 4wd at the beginning and that is why they are rolling forward. I then hear a snap once he starts to spin. I could be wrong though.