A fire tornado develops on the periphery of the fire! Consequently the wind interacts with the inflow on the other side causing spin. Obviously the side by side shear creates a tornado combing with extreme heat.
I wonder if this is the type of tornado caused a fatality a few days ago. However we know that may have been stronger. This is spectacular but rather scary. Interesting to see just how the low grass got singed sideways. Did you notice the fire inflow jet coming around the side?