Seconded. Following a class syllabus on your own time and without grading or feedback except knowing whether you did it is under-rated :-)
That's awesome. It's very well written. In just five minutes of reading, I learned what registers and memory-mapped I/O are and how they apply to the Pi. Old news to CS students but for this guy with a liberal arts degree, super helpful. I'm grateful that the document took the time to explain this kind of thing.
Did you complete assignment 0 yet?
If you follow the pre-registration survey link, it asks for a SUNet ID, and if you try to register via Piazza, it asks for an @stanford.edu email address. So it seems likely the course proper is just students.
FWIW I created a subreddit [0] for folks (not from Stanford) wanting a forum to study, follow and discuss on this course.