Maybe it was a BLEVE, boiling liquid, evaporating vapor, explosion? Liquid doesn’t actually burn it has to turn into a vapor, which happens at vastly different ambient temperatures.
Yeah it looked like a vapor that escaped first, forming a cloud, then the fireball exploded behind it quickly overwhelmed what looked like the vapor, you can see it kind “eat” the vapor cloud, but I Think it just looked that way as the gas spread out quickly with the fire chasing it and combustion it.