The handle was not all the way in and snapped into the lock groove and putting the breakaway cable over the handle should've given him a clue if he wasn't so green. He should've done a tug test for sure but the problem was already very obvious. I used the two jaw drawtite for over 20 years and I thought it was a great hitch because the handle would snap all the way in when the jaws were home. It's always a good idea to make sure the pin box is slightly lower than the hitch so that you don't have a high hitch problem. That design is a heck of a lot more fool proof than the B&W hitch I use now. It also looked like there was a lot of rust on that hitch so who knows how sticky it was.
I bet he knows how to use that hitch now !! Craig