Question about skipping the staging area

The video “Skipping the staging area” on Chapter “Creating Snapshots” introduces the command:

git commit -am "message"

By doing some experiments, I came to the conclusion that git doesn’t actually skip the stagging area, but will stage only the tracked files and commit them in one go. So the difference between “git commit -am” and the 2-step process of “git add . followed by git commit -m” is that the first will not add untracked files but only stage the tracked ones.
Let me know if I misunderstood something.
Excellent course btw! Good job!