Negligence, in the context of that quote, is a civil liability/law of tort concept. Civil law has a lower evidential and liability threshold than criminal law. While it may be fair to expect an insurer to pay up for a pedestrian that mindlessly steps in front of a car, the same would not stretch to criminally prosecuting that driver and imposing a criminal sentence. This is also why the word gross is added in the context of gross negligence manslaughter, meaning the negligence must be reckless or egregious. This is a distinction we must make here.