11:11 PM, Thursday January 14th 2021
I think you're slightly misunderstanding. You don't just draw the shadow the form casts on what's around it, but also them shadows cast on the form itself by its own change in shape. In your nose example there will be shadows on the nose where it turns away from the light. These should be included and should describe the form without an outline.
That is unless I'm the one who's misunderstood. I'm still working on the texture section myself, so perhaps someone more experienced can way in to verify/correct what I said.
Edit for clarity: I read the quote
"Instead of drawing the forms themselves, you should be drawing the impact they have on their surroundings - that is, the shadows they cast."
as saying "cast shadows instead of outlines" rather than a statement that you shouldn't shade in the shadows of a form, as that would not fit with the demonstration.