It's treating "student" as the individual's current occupation, which seems reasonable. But if you are conducting your own unaffiliated independent study that eats up most of your workday, you can probably get in touch with them and get a waiver.
You absolutely can! I used to teach an informal free class on CSS (http://magicofcss.com). Even though I wasn’t a teacher at any actual school GitHub kindly gave me and my students access to free private repos for educational use. (See https://education.github.com/guide for more information.)