I /think/ I found a typo in the course material. I only found it by chance. The Exterior Course material says
The footing near the home may not be placed on undisturbed soil. Some codes
consider soil to be undisturbed if it hasn’t been disturbed in more than five years.
When I download the How to Inspect Decks document, it says
The footing near the home should not be placed in disturbed soil. Disturbed soils are
those which have been altered as a result of grading or construction, etc., giving the soil
From what I’m reading online, it appears the “Decks” course is wrong.