That's really rare. Back when I was in school the professor who taught the class and wrote the book would, every year, change enough of it to sell a new addition. Either move the sections around or change the problems.
Just so he could make more money.
It was a calculus class.
Fuck him.
Oh god....
Copy left is not a protected term but yeah this is a shit license.
And how the fuck do you contribute code back without forking the project?!
EDIT: It looks like an issue has already been created and I absolutely love this thread where the license they are using is in violation of Github TOS.
They should have just kept the source closed! The speculation is that whomever purchased it wants to crowdsource contributions without adding any value themselves.