No, Anders Breivik is not a Christian, anymore than a person born in a garage is a spare tire. Amen.
If you really want to get technical, a Christian is just someone who believes in the divinity of Jesus. FWIW, guys like Torquemada and some of those corrupt Renaissance popes were Christians as well, albeit not very good ones. That said, I’m still a bit doubtful of Mr. Brevik’s beliefs, inasmuch as he lives in a country where 2% of the population attends church services.
I personally am inclined to agree with some of those on FR who proposed that Savage refers to him as a Christian extremist because A. he’s Jewish and thus it costs him nothing to make this claim and B. Mr. Brevik was anti-multiculturalism, a viewpoint that Savage has in common.