I’m sure he wasn’t. Which is where negligence comes into play. Just because you did something and didn’t mean does not make it ok.
The difference here is that if he meant to do it, it would murder.
If he did it, didn’t mean to do it, but was high/drunk, it would be vehiclular manslaughter.
If he, did it, didn’t mean to do it, and he was not high/drunk, it is involuntary vehicular manslaughter. Which is this case. It is a lesser charge but he should be charged with it.