If you were driving your truck with no issue not realizing the axle shaft was broken then your locker was definitely engaged. Because otherwise your truck would not drive with a broken shaft. Your truck would act as if its in neutral with a broken axle shaft. (unless you have the truck in 4wd)

 

yes its 4wd

 

Yes but were you driving it in 4wd? Because if not, the truck would literally not move with a broken rear axle shaft, unless the locker was engaged.