Apparently for that specific type of ADIRU, Airbus has substantially modified the checklist in response to an Inertial Reference fault. It is now question to turn off both parts of that unit : IR + ADR
Due to the nature of the fault in the ADIRU 1 "random spikes" it is hard to say if the crew had the proper tools to determine if the ADR part was at fault too and to turn it off before the sudden pitch down ?
How strange is it, the protection which is supposed to protect, sent the pax through the roof, and for no good reason !?
That Airbus is a VERY complex machine …