JimL,
If we don't need to know all this stuff, why does the CAA have those horrid umpteen dozen written tests that Pilots have to master before obtaining their License?
Seems like a bit of a radical view you hold compared to the CAA's Official Policy.
Fog is a ground based Weather Phenomenon as I recall and thus is not "Cloud".
The only thing that would matter would be the Viz that night which was reported to be in "Tens of Meters". The only criteria (it seems) is if the PIC observed what Viz there was and was satisfied it was 150 Meters or more.