On this website, I often talk about the Jesus Myth Theory, as if there was one and only one interpretation. That is not quite accurate. There are at least three forms that the Jesus Myth Theory can come in.
Non-historical and pagan-based
This is what many people think of when they think of the Jesus Myth. This view sees Jesus of Nazareth as not being a historical figure. Not only that, the Jesus of the Gospels is a borrowing and altering of existing pagan gods/heroes.
Historical but pagan-based
I need to be careful when I describe this view as being historical. What they mean is that there likely was a Jesus of Nazareth, perhaps born of Joseph and Mary and he may have been a Jewish religious teacher. But they think most of the details in the Gospels come not from the historical Jesus but from pagan myths.
Non-historical but not pagan-based
This view would reject a historical Jesus. They would add to C.S. Lewis’s trilemma, a fourth option: legend. The story of Jesus in the Gospels is a myth. But they don’t necessarily see it as a direct borrowing from the pagan myths. Jesus was a new myth being introduced to the world.
The point of all this is that when talking to a Jesus Mythicist, take the time to find out what they actually believe. Don’t assume you know because they identify as a Mythicist.
