Did you vet this article? Maybe things have changed since it was published, but the MIT OpenCourseWare site explains it clearly in the footer on its site:
"MIT OpenCourseWare makes the materials used in the teaching of almost all of MIT's subjects available on the Web, free of charge. With more than 2,200 courses available, OCW is delivering on the promise of open sharing of knowledge."
So they basically openly publish the syllabus, etc and provide links to Amazon for the textbooks used in the course, but the things linked in the article are not actual courses that someone can take for free.