but what is "Open"? There is also an article about "What is Open" concerning APIs : http://api500.com/post/44022221316/what-is-open

Openness for APIs is about to be Accessible, to be Public, to be Neutral and to be Re-usable without restrictions.

So to be Public is one of the part of to be Open, in my opinion of course. Some people have made a larger definition about openness http://opendefinition.org/okd/