Perhaps:
- Guard is cut-off inside the box, to prevent guard loop.
This could be all it is for all we know, unless someone has one to open up and check. It honestly wouldn't surprise me at all if it is just the a way to bring the force/sense high lines together minus the guard so you can plugin to other equipment using the rear terminals.
I just made the equivalent of this thing last week so I could calibrate an old R&S power supply.

Cost ~$20 in parts. I have no doubt R&S also charged a silly price for it like Keithley is doing with this thing.