Wrong there was a gap at the drivers side. Look again.
Every high pin I've seen with rv and non rv trailers and 5th wheel hitches looked just like this. There was no big gap all around but one side or the other or to the rear of the hitch plates.
IMO the guy in the you tube may never know what his exact scenario was that lead to his dropped trailer. But he may have a couple of good guesses which will lead him to better hookup procedures.
Those that think their brand of hitch or jaw type can't be high pinned....high hooked....high hitched or whatever term you use are just fooling themselves ...which makes for good joking over on haulers forums where those folks that use products/equipment daily know better.