the common mistake is people thinking Catholic and Christian are identical.

Catholic is a distinct subset of Christian. So all Catholics are Christians, but not all Christians are Catholic.

Christian is any member of religion based on the teachings of Jesus Christ. This includes all the weird mega churches that have no history, and get created by money hungry preachers who have no real expertise in religion. It also includes well established traditional forms of Protestant Christianity - Methodist, Anglican, Baptist, Greek Orthodox, etc. (about 300-700years old).

Catholic is any member of the Catholic Church, which has a very distinct interpretation of the teachings of Jesus Christ, maintained by its network of Catholic churches all over the world, which is under the control of the Vatican, which is under the control of the Pope, who is supposed to lead Catholics as Jesus would. The Catholic Church is about 2000 years old.

The common problem that arises today is when uneducated rednecks that join some weird brand new church which is technically Christian, and some weirdo uneducated backwoods preacher tells the congregation that evolution is a lie and everything in the bible should be interpreted as a literal fact. Then his congregation gets all wound up and runs around saying that they're against evolution because they're Christians. Then people who don't understand the distinctions between Christian religions assume that all Christians are against the theory of evolution. Then you see all these science-lovers think that they have to be atheists and fight for atheism because they think Christianity is against science, when in fact, the Catholic Church and several other forms of Christianity fully embrace science and are actually major proponents of it through the schools and universities they've created over the centuries.

And that, my dear Redditor, is why it pains me when people don't understand the distinction between Catholic and Christian.