It looked to me like a combination of miracles that allowed Roman to escape the destruction his car experienced.
It appears the front tires and suspension which were ripped from the chassis enabled the spread of the Armco which allowed the cockpit to pass through the barrier intact thanks to the strength of the Halo device. If I recall from the video there was no part of the cockpit higher than the Halo remaining. Lastly and in my mind the final miracle was the 28 seconds in the fireball and the hot gasses. Was he able to hold his breath? Gas temps were not blue flame hot but certainly fatal hot had he inhaled them for that length of time.
When he appeared out of the flames on his own power we were witnessing a culmination of miracles, as in difficult to understand, but grateful for the result. Hopefully he will be able to share what he remembers with those who operate vehicles on the highways of the world. We face much less impact forces in accidents, but the experience dealing with the circumstances can be beneficial for everyone who drives.
The Nosecone parted the ARMCO row 2-3 (bottom & center) and the slope up to the HALO allowed the combined hardware is what mechanically saved Romain.
Race Cars are way safer than street Cars.
Did You know Romain has a Cookbook available ?
https://www.amazon.co.uk/MARION-ROMAIN-GROSJEAN-CUISINE-CONFIDENCES/dp/2956287206