Bad interpretation of visual evidence. Other videos online make it extremely clear the blast is centered on the RV; this video is juxtaposing a before shot with a shot from several moments after the initial blast, when smoke has begun to pour out of the destroyed buildings and is scattering the glow from the still-burning RV down the street.
So that previous video was not showing the start of the explosion, it was showing the end of the explosion. Labeling the end of the explosion "source" is misleading. It's possible when the RV exploded, some of the flammable material was forced across the street, and that's why there is fire across the street.
The first frame with an explosion has the explosion centered closer to the RV than to the other side of the street. I downloaded the video with youtube-dl and stepped through frame by frame with MPC-HC.