Are people who are born Christians but become atheists regarded as Christians by Muslims?

If someone was born a Christian, but decides that God doesn't exist, Jesus was an ordinary human being, and that the Holy Spirit doesn't exist, and becomes an atheist, are they still perceived as Christians by Muslims? Someone tweeted today > Atheists who've repeatedly insulted Christians draw a cartoon of > Muhammad, so Muslims burn down churches. Go figure. > http://www.bbc.co.uk/news/world-africa-30863159 … and I wanted to know if the categories of "Christians" and "Atheists" make sense. Related question: https://islam.stackexchange.com/q/11400/301