From musician/videographer Amy Sanchez's description on YouTube:
As we drove through, the strong wind was pushing the flames into our lanes, and you can actually see embers sparking up the windshield of the car. I believe this fire became the Anaheim Hills Apartment fire which you can see at the end of the video. And yes, one of the passengers was on his cell phone the whole time…
And for those wondering where (and why) Mr. Shostakovich comes into all of this:
I chose this music for several reasons, but mostly because we were actually on our way to perform this piece at the Riverside Philharmonic concert that evening. We found it interesting that the music we were about to perform matched the intensity of the fires we witnessed.
On top of that, she quoted musicologist Robert Dearing, who called the second movement of Symphony No. 10 as "a study in concentrated fury rarely equaled in music."
I believe it. So will you after you've seen it:
I wish I knew which recording she used; I'd buy it.
And here is KCAL–TV/9's report on the finished video itself: