“During the first three Christian centuries, the practices and beliefs found among people who called themselves Christian were so varied that that the differences between Roman Catholics, Primitive Baptists, and Seventh-Day Adventists pale by comparison. Most of these ancient forms of Christianity are unknown to people in the world today. In the second and third centuries there were, of course, Christians who believed in one God. But there were others who insisted that there were two. Some said there were thirty. Others claimed there were 365.”
"Lost Christianities" by Bart Ehrm
Types of Christianity in History: Who Were the First Christians?
And not all followers of the teachings of Jesus were or are Christians. (Just as (IMO) not all Christians were or are followers of the teachings of Jesus.)