Spoiler Warning: The following bookmark contains some plot information relating to The Crossing.
The description of the elderly Indian man suggests he may be a shaman or medicine man. It is this man who correctly identifies Billy as 'huerfano' (an orphan), the truth of which is only later revealed.
McCarthy frequently uses mysticism in superstition and dreams to communicate knowledge a character has no rational way of knowing. In The Crossing, it suggests the existence of some deeper world, a universe possessed of some inner logic that lies just beyond human understanding.