Read this
I read most of it. This post is open to all so the use of the word Christian is open ended. If you are going to examine a small group usage of a word it needs to be precisely presented.
Do Catholics believe in Christ? This is the root of the question as I see it.
They were first called Christian in Antioch. The word meant someone who follows Jesus and His teaching. Catholics don't simply follow what Jesus taught. They have added to it, twisted it and come up with their own religion. Catholic are followers of the Catholic Church and what it teaches.