I guess if Guest is relabled "Can View Private Class Info" then the structure starts to make sense to me.
The roots of the Guest role lie in the legislation Dee mentioned above, which defines privacy requirements for Universities at least (I don't know the full scope of the amendment). So you're on the right track with the above sentence.
As to "guest profs" and all the various combinations that are allowed , I'll leave that to Dee or OF folk to explain. :)
