It's not clear what the circumstances are eg was the farmer breaking the law by the bill being turned out alone in a field with a FP, or had there been previous incidents with the animal which meant he knew it was high risk temperament.
If not, then from a farming POV it is worrying, as normally while there is civil liability for any accidents and injuries (dealt with by insurance), there shouldn't be criminal charges,
Which makes me think, and hope, that the circumstances of this case might have aggravating features, if not it would be of great concern.