By his own words he acknowledges that he is not a christian. What he does in his manifesto is he creates new definitions for Christianity. For instance, if someone declared themselves to he a homosexual who is not attracted to a person of the same sex but is attracted to members of the opposite sex, then no matter how much this person declared themselves to be a homosexual, they wouldn't qualify.
Breivik's own words:
If you have a personal relationship with Jesus Christ and God then you are a religious Christian. Myself and many more like me do not necessarily have a personal relationship with Jesus Christ and God. We do however believe in Christianity as a cultural, social, identity and moral platform.
He's declaring that there exist two categories of Christians, those who are religious and those who admire the cultural, social,identity and moral artifacts which arise within societies which are dominated by "religious Christians."
There certainly is a category for people who qualify under his definition but they're not Christians. They'd be better described as Westerners or Post-Enlightenment adherents, or Western Civilization fans.
He's as confused as that nutty Christian preacher who thought she could simultaneously be a Muslim.