"Justin Webb granted the licence, "

Except it's used under license from naturalmotion, and naturalmotion owns the code (hence the copyright naturalmotion).

Yet, naturalmotion explicitly grants no rights.

I can state affirmatively this makes no sense :)

As I said, either they've granted rights (through justin), in which case that statement that they grant no rights should not be there (because they are in fact, granting rights) Or they haven't granted rights (through justin), in which case it's not open source and who knows what rights you are getting here.