The gas is heavier than air and has a white vapor, which is why the people filming the incident were able to spot what was about to happen. Many motorists pass by the gas leak, oblivious to the danger. Unfortunately, one lingers a little too long and gets caught in the blast.
After closely analyzing the video, we've come to the conclusion that the silver car right next to the tree is the source of the fire, most likely the gas reaching its hot exhaust pipe. You can see the flame spreading from underneath the car to the LPG reservoir. Just before that, an employee of the gas station can be seen running out towards traffic in order to stop it. This is the right move to make, as the explosion could no longer be contained at this moment.
Everything happened somewhere in the Republic of Dagestan, a federal subject of Russia located in the Caucasus. They have a number of fake gas stations there that plagiarize global brands, which is why this one is called EXSON, not EXXON as it should be.