Talking with a guy who explained how this was true.  You can read the article but I can condense it:

Warming a few degrees has caused the pine beetle to survive winters.  They have migrated north and drought ravaged trees lack the ability to fight off the attacks of the beetles.  The dead trees burn much better than green trees and their dry leaves are extra fuel.

https://www.cbsnews.com/news/how-the-bark-beetle-fueled-californias-wildfires/

Another study disputes the pine beetle as a contributor;

This one from https://www.sciencemag.org/news/2015/03/tiny-beetles-don-t-cause-big-fires-study-finds-raising-policy-questions

“We were looking to see if there was more area burned in forests that had been infested by mountain pine beetle rather than the live forests,” says lead author Sarah Hart, a University of Colorado postdoctoral researcher.

The result, Hart says: “We did not find any difference.” Specifically, the researchers found that beetles had recently attacked just 5% of the more than 100,000 square kilometers of forest that burned during the 2006, 2007, and 2012 wildfire seasons.