The current Indy car is actually extremely robust, as anyone who has witnessed many of the crashes will agree.
However there is one vulnerability, which is the open cockpit.
It appears to me looking at the replay that the topside of the car went into the catch fence and likely his helmet hit one of the fence uprights. You can see the impact if you watch in slow motion.
Here is a post crash picture showing the damage.
http://www.openwheelworld.net/photos/original/vQ6hoyzL19639.jpg
Good eye.
I watched the YT clips over and over and lose track of who is who in the smoke, sparks,debris and fire.
