Black is (not always) black

Lesson 2 in a photography course is all about how modern cameras with their oh so clever auto settings aim to make your pictures 18% grey. This week's homework was to take a black on black photo (& a white on white) on auto and then identify the 18% greyness & edit it out...
I'm hoping that my attempt to interpret this challenge with white on white explains the conundrum to me, 'cos currently I'm flumoxed*.
The 1st pic is unedited from my Panasonic on its clever auto setting, the 2nd from my Nikon on auto & the 3rd is edited to my taste from the Nikon.

There might be 50 shades of grey, but I reckon there's just as many shades of black.

* this could also be due to the fact that I came this close (am holding up fingers a hair's breadth apart) to being T-boned by some stupid witch** who was determined to pull out of the junction I was turning into.

** well it rhymes with witch