Not a US citizen, but AFAIK, a course includes lectures, office hours, assignments etc. How did he manage to fully understand the materials without all the resources that are provided only for registered students?
As for office hours, I never went to any, but I assume that they're not going to check your student ID, just as they don't check before lectures.
Tutorials were run by TAs recruited from the body of PhD students and so could be of mixed quality (my metaphysics tutor was better than the lecturer), but would at least have value in repitition.
Libraries were vital to me. As at the time were computer facilities (MathCAD, Maple, Excel, Fortran, etc.). For some of my courses there were laboratories (material science), and for Art History there were trips and a special picture library.
You could sit in the back of lectures back then, but I think they check your ID nowadays.
Preach it. The same is true of past or specimen exam papers or textbook questions. Writing, like debating, exposes your own ignorance to you and allows you to remedy it.