See step 6. The view is pulling the cache key straight from the domain model. It relies on being the informed as well about changes in its children to do that, which is what the setup in step 5 is about.
So you save the render plus any db calls that would be triggered as part of that render.
I can't believe I didn't think of this before. My initial reaction after I skimmed the post was "uhh, so you still hit the db? what's the point?"
Thanks for sharing this! I definitely want to implement something similar for my future projects!