There's free, then there's free
Interesting, Giving Knowledge for Free is, well less than free. It's free in the sense that the work doesn't cost you anything, granted; but it appears that you need permission to reuse, remix, revise, and/or redistribute their work.
I understand there are degrees of openness, but the least someone could do if they are going to write an article, book, etc. about open educational resources is to make the work itself as open as possible (e.g., CC, CC-BY, etc.).