Unless he somehow spun the car and went into the tree tail first, a ruptured tank is highly unlikely.
We had a horrendous crash in my area where a street racer rear ended a much slower car, destroyed the car, and killed a little girl, but there was no fire at all.
He will be spending quite a few richly deserved years in jail, by the way.
I saw a video of the scene after the accident and it appeared that the car sheared off a fire hydrant before striking the tree. Someone speculated that the metal fire hydrant could have ruptured the fuel tank which allowed fuel vapors to ignite from a heat source such as the catalytic converter. I'm not suggesting that foul play was not involved.
What about the fire hydrant he ran over just before he hit the tree ? Could such a large metal object have ripped open the fuel tank? Isn't the fuel tank usually located in the rear of the car behind the wheels at the bottom of the car?