You aren't actually debating anything, just being extremely pedantic about legal terms that often mean different things in different states and countries. There's no reason anyone needs to reference a specific murder charge to call this murder-- murder itself at its most basic level means an unjustified killing. But legally speaking, murder is often referenced in this exact situation: depraved heart murder or third degree murder.

Vehicular manslaughter is another very specific legal term that only exists in certain places, so it's unreasonable for you to expect people to change their colloquial definitions of murder based on that. Even so, this is likely going to be far more serious than vehicular manslaughter-- which is what it would have been if the driver actually stopped and called 911. The fact that they drove away really bumps this up to potentially some kind of legal murder charge, and colloquially at least it is perfectly accurate to call them a murderer.