The black box holds a fuse, in case the positive charging lead somehow shorts out to the frame. I would want that!
The female side of the connector goes to positive on the battery, male to ground. The female is recessed in the rubber and won't short to ground unless some metal bit pokes into it, pretty unlikely.
Not as unlikely is setting the centre stand leg on the cable and crushing though the insulation, or some accident where the wire is cut into by a sharp metal edge.
The charging wire will melt and flame in a second or two with a solid connection to ground and a charged battery.