The question is still not answered. It does not matter if it came from this mistake, an engine defect, another vehicle around the airport, blown into the grounds etc. The designers of the aircraft and the operating procedure for the aircraft must take into account the chance of the occurrence. Materials of this type have been, and will be, found on the runway. The aircraft must be designed to either survive such occurrences or methods implemented to stop them occuring.
This was not the first time the tyres of the Concorde has damage from impact, nor the first time this type of metal had been found on a runway. It was not unreasonable for them to foresee such an occurrence. It was negilant to operate an aircraft in such a manner knowing it was susceptible to this issue but not take action to avoid it.