It does, and I’ve read that before. I can see the argument, but it’s not that unusual IME for there to be handful of witnesses and not all be asked for statements when there is either forensic evidence or a general agreement on what happened. If, for example, all the witnesses said ‘the driver seemed drunk’ but in fact she wasn’t, would it matter that they’d all been interviewed?
If the investigation focused on the data from the car and driver’s phone, excluded drugs or alcohol, received a legitimate medical report and investigated prior medical history, it could be legitimate that they didn’t interview everyone at the scene.
I don’t think we know for certain who was or wasn’t interviewed - AFAIK the former head has expressed surprise that she wasn’t interviewed but hasn’t disputed apparent evidence from other witnesses who say driver was disoriented and had bitten through her tongue. (Not certain if that’s factual or speculative either tbh).
It could be that the failure to interview is part of the misconduct but doesn’t in itself change the known facts.