Aborigines traditionally adhered to animist spiritual frameworks. Within Aboriginal belief systems, a formative epoch known as 'the Dreamtime' stretches back into the distant past when the creator ancestors known as the First Peoples traveled across the land, creating and naming as they went. Indigenous Australia's oral tradition and religious values are based upon reverence for the land and a belief in this Dreamtime.
The Dreaming is at once both the ancient time of creation and the present-day reality of Dreaming. There were a great many different groups, each with its own individual culture, belief structure, and language. These cultures overlapped to a greater or lesser extent, and evolved over time.
It doesn't sound like an easy task to reconcile those kinds of beliefs with Christianity, but I suppose he managed to do it, and I hope to track down the book to read the story of it. What an amazing point of view he must have had.