clever editing, but also deceiving. The overlay darkens the shot, almost masking the dust/debris/smoke cloud that is traveling outwards from the explosion, blocking the flames from the RV-outward. what we are seeing is just how far out the flames got from the RV.

You definitely can't say for certain where the explosion came from based on any of the videos I've seen. Seems like a person would have to look at the crime scene for more information.