I don't know if the conflation is exactly that but proponents of materialism have long been accused of atheism for a long while on the belief that materialism is incompatible to view that God and other spiritual entities are incorporeal, specifically in Christianity. Thomas Hobbes, for example, held the view that God, as well as heaven and hell, as corporeal, i.e. material bodys in motion, and was accused of atheism.

A central belief in Christianity is that Jesus Christ was 'made flesh' when conceived in the womb of the Virgin Mary, so this would suggest, though Hobbes might've disagreed, that the second person of the Trinity changed from immaterial to material, i.e. incarnation.