“Pilot Error” was not one of the choices available. If it’s judged to be their fault the possible “verdicts”;were:
1. Error of judgement
2. Negligence to a minor degree
3. Negligence to a gross degree.
The relevant document had definitions of each but I can’t remember them . I believe there is a record somewhere of Wratten directing, prior to this event, that if an aircraft crashed it was because someone had been negligent, or words to that effect.