Ok, so what else is it? My understanding that the new Go language is not officially called object-oriented because it supports only interfaces and not inheritance or type hierarchy.
If you really want to know what OOP is / was / can be, read Cardelli and Abadi's A Theory of Objects. The first half is available online, and covers the parts you'd care about: http://books.google.com/books?id=4xT3LgCPP5UC