Ian Anderson was just a balding guy with long hair. It's not any kind of fro, really.

A Jewfro just comes from the fact that many Jewish people have curly hair that often resembles a small afro. I'm not sure if there is any definition other than you have to be Jewish to have one, I wasn't aware that it extended beyond Jews. My understanding:

Black guy with an afro=afro

White guy with an afro=afro

Jewish guy with an afro=Jewfro

Although the Jewfro is usually much less intense than an Afro. Afro's are more deliberate, and an actual fashion style. Jewfro's are usually just an unintended consequence to having curly hair.