The melted aluminum that I saw in that fire and many others was from burned up cars. Houses burn pretty hot but not that hot. The trees were not nearly as flammable as the cars and houses.
If the aluminum came from the cars then the tires probably ignited and those would burn hot enough to then melt the rims.
One of things that strikes me as unusual is how far the molten aluminum flowed. In some cases, maybe as much as 8 feet or more, if you look at the video I posted above.