You cannot set the visibility options (course, institution, public) for individual pages, only the course as a whole. The "customize" options in course visibility settings allow you to set granular visibility for files and/or "Syllabus" but not pages. There are times when there might be a useful page that an instructor wants to share publicly.
Ideally, it would be possible to set visibility on a per-page basis, within the page's Edit settings. As a second, less ideal option, just add "Pages" to the Customize Visibility options in Course Settings.
