The cauliflower-like lower cloud is known as a pyrocumulus and is generated by the intense updraft produced by strong heating in the fire. It is likely composed of smoke, ash, and cloud droplets. The latter form as the air rises and cools, with water vapor released by the burning of fuels that contain water also contributing to the water budget. In some cases, pyrocumulus can produce lightning and thunder.
The pyrocumulous is topped by a more fibrous pileus cloud. Pileus clouds are similar in appearance to lenticular clouds that form from the interaction of flow with mountains and hills (sometimes called wave clouds). The pileus cloud, however, forms when an intense updraft forces a layer aloft upward. They can be produced by convective clouds, volcanic eruptions, and thermonuclear explosions (fortunately, these are banned today, but you can see examples in historical footage).
|Pileus cloud during eruption of Sarychev Peak in July 2009.|
Source: NASA/JPL and Wikipedia Commons.