This exercise compares photographing black, grey and white tones with the camera first in Program mode and then in Manual mode.
We can see the camera does not have enough information when photographing a single tone to correctly show that tone. This means that photographs showing solely black, white or grey will show very similar histograms. When you photograph all 3 tones together, even though still in Program mode, the camera can detect the difference between the shades and reproduce the shades more accurately.
Switching to Manual mode allowed me to make the camera underexpose to get more black and overexpose to get more white. This happens in real life when trying to photograph snow or pregnancy tests, for example.