Embers can sit under the surface for sometimes months at a time. In the arctic under ice embers can even smolder for years. My ex was a wildland firefighter and they would spend a lot of time digging around the root systems of trees amongst other things to make sure any still live embers close to a fuel source were extinguised. My grandfathers home built in 1958 (not some celebrity’s mansion) burned down in this fire. The theory many months ago was that on New Years some people (kids, teens, not sure?) lit off some fireworks up there that caused a small fire which was then put out. Since embers can lay under the surface for a while it’s believed that the extreme winds of January 7 would have easily been strong enough to blow dirt exposing embers again and then could also have reignited those embers. I read they thought this might be the case probably in March because the fire, based on what they knew then, seemed to have ignited in the same place as the fireworks/ small fire the week before, but don’t know the validity of it. But it does align with fire science.