It certainly looks like the entire HP Turbine blade mount went! A blade, albeit the front fan being rather large, is designed to be contained by the casing. I really don't think any engineer is going to be able to design an engine with competitive power to weight ratio that could contain something like a turbine mounting disc with the energy contained within.
Obviously, IF that was the cause, then the investigation needs to look at why it failed as the hours on these engines can't be all too long.
As to shutting down the engine, if the Fire disconnect push buttons failed to cut off the Hyd, Fuel and electrics then something needs a serious look at! If the failure of the engine was in the rear of the core, as the pictures suggest, then there is always the possibility of high speed spin from the main fan.
All conjecture as the only true cause and consequence will be from the official report.
Good job by the Flight Crew though, must have been an interesting day in ECAM world!!!!