Based on wildfire statistics and common causes of wildfires, the most likely cause of the Smokehouse Creek fire is:
sparks from a downed electric line.
While lightning strikes can initiate wildfires, in many cases, especially in areas with human infrastructure, downed electric lines are a frequent cause of large wildfires. Other options, such as heat from the sun and magma from a local volcano, are less directly associated with sparking wildfires.