Earlier quoted context omitted.
Fatal vehicle accidents are not always vehicular homicide/manslaughter. A standard of negligence (such as being past the DUI limit) has to be established. Hit-and-run also does not necessarily result in a homicide (or assault) charge being filed.
Someone struck him with a car and killed him. I think leaving the scene after killing someone with a vehicle should satisfy any any standard of negligence.
In terms of the hit-and-run == negligence...the two things correlate...a drunk driver may be so drunk that they don't realize they've killed someone. Or more maliciously, they do realize it but don't want to take a breathalyzer at the scene of the crime. However, there are cases (which does not seem to apply to the case in question) in which otherwise well-behaved drivers have killed someone unknowingly or for some reason panicked and left. It's still a crime, but it's not "homicide"