includes the skills for a Class 4 instrument rating/night.
And the Class IV instrument rating did not authorise flight under the IFR. That's why the department of many names changed the title to NVFR.
The minimum skill required is
one 
night landing at a dark aerodrome with no horizon. Hardy enough to let people loose on a dark, dark night. And no requirement for a takeoff with no horizon, and that kills a couple of people every few years.
If there is no discernible horizon and pitch black it could be successfully argued that it is not VFR.
No it can't be. That's a non-sequitur argument.
Similar to fog in daylight and irrespective of cloud.
Que? Fog is a type of cloud, reducing visibility and clearly impacts on VMC visibility. Perhaps you are thinking of the polar whiteout phenomenon (which is not related to cloud).
You need IFR skills to operate at night with no horizon. To fly in those conditions, I believe that one should have the minimum experience as for an IF rating (without the approaches). The PIFR perhaps - I'd have to look at the syllabus.