Without going on too much of a tangent,
The fire started perhaps a half mile behind the group of people watching, and generally went from west to east, the direction of the wind. In the last photograph, one can see there ought to be a natural firebreak with train tracks and a tidal stream. The first two photographs are of the street (Canal St.) just to the east of the tracks. I suspect that embers landed on the rear/front porches of the three deckers. Its because of disasters such as this that building codes and fire codes are revised.
My grandparents house was built on a street that burned during the fire; built shortly after the fire as a single family detached, it had ugly, asbestos shingles as siding for decades.
^^^ One of the first aerial news photographs of a disaster.