One of the through bolts could have come out, fatigue (crack) failure of the arm structure itself, ball joint, etc. If I remember right it was all torn up pretty bad on that corner, with that violent of a shunt it is really hard to figure out exactly what broke and in what order even if you had the time to thoroughly inspect the pieces, I didn't.
I helped do tech inspections a few times for a west coast cobra oriented event and was struck by the single roll over hoop design used on many cobra replicas. I asked a few guys what they though about their roll hoop design/ potential effectiveness. Mostly blank stares were the result. There is a reason the factory five challenge series cobras have a full A + B pillar box cage with many cross braces and gussets.
I posted this video again, yes Rick it is a few years old, to add to the discussion on roll cages. Track cars would be a yes IMHO. Street ONLY cars would be better served with a firmly braced, rear only, full width hoop. Its the dual use cars that are, or can be, a real problem. I Looked at different styles of head protection, including rugby helmets and other associated sports head gear, for street use in such a car but never came up with something.
In any case, Ya really lucky.............