Yes, I saw that one live and just like everyone in the pits, assumed he was dead already, or going to be very soon... The broadcast I watched didn't stay focused on the car for more than a second or two after the impact and flames, and then only on replay showed him getting out.
Stenhouse was really relaxed though! Do they have a helmet air supply? I guess it is better to just undo the belts like normal if you can't see them.
Another thing about the Grosjean crash that is easily overlooked due to the fire, is that the HALO saved his life.
If you watch the Youtube video, "Grosjean Fireball Crash", and freeze it at the 1:21 mark, you can see where the HALO cut through the middle piece of ARMCO, and bent the top piece high enough for him to pass harmlessly underneath it.
(The front part of the car punched through the bottom piece). Without the HALO he would have been decapitated almost exactly the same way Francois Cevert was, in practice at the 1973 Watkins Glen Grand Prix.
That race was supposed to be Jackie Stewart's final race before retirement. Cevert was Stewart's teammate, and was scheduled to take over as the lead driver for the Tyrell F1 team after he retired.
But Stewart was so shaken by the horror of that accident, and the damage to Cevert's body, he refused to race. (They left his headless body in the car for several minutes, and many photographers took photos of it).
Those photos are all over the Internet, and that accident is regarded as one of the most violent in open wheel racing. The Gordon Smiley Indianapolis crash possibly being the only worse one.
There was another driver killed in that same manner in 1974. His name was Helmuth Koinigg. (The car slipped underneath the ARMCO decapitating him).
Grosjean's accident proves just how far safety in car design has come in all of that time. If his accident had occurred just a few years earlier, (pre HALO), he would have been killed.