It's a bit dumbed. But DfT are themselves very wary of the data on causes so don't use terms like fault or blame. I don't know why the BBC have written 'drivers' fault' in inverted commas like it's a quote because that term doesn't appear in the data release. DfT talks about 'contributory factors' quite deliberately and advise caution in interpreting the data. They say:
"Contributory factors are designed to give the key actions and failures that led directly to the actual impact to aid investigation of how accidents might be prevented. The factors are largely subjective, reflecting the opinion of the reporting police officer, and are not necessarily the result of extensive investigation. Some factors are less likely to be recorded since evidence may not be available after the event. While this information is valuable in helping to identify ways of improving safety, care should be taken in its interpretation."
So, they don't make the jump that because an officer notes that someone was wearing dark clothes at night that they were to blame but it is noted as contributory. Also, officially, they are not accidents. Accidents are blameless by definition. They talk of collisions and incidents.