It's probably defective piece it should not come off that easy. Also it probably won't be a water proof connection when you tighten it up it will probably pop off again.
I would say yes it does snap back on but the question is......That O-ring does it have to be in the groove of the nut before it gets snapped back on or is the o-ring slide inside after you snap it back on. I guess this happened from overtightening the nut/collar?
If nobody answers your question I will look when I get home in a few hours at my Equinox and Manticore connectors and post back.
I looked at my connectors, it should pop back on and then slide the o-ring over the connector part into the collar/nut. Like C-COD said it will probably pop off again and probably no longer safe to submerge in water.