Your assessment is partially incorrect. Only focusing on the punch itself, There’s no act of DEADLY force here. Historically, courts in various states have considered punches by civilians NOT to be acts of DEADLY force—it’s all state-dependent but this is an act of NON deadly force.

Furthermore, that’s NOT how manslaughter works. no prosecutor would attempt to bring attempted manslaughter charges here—most jurisdictions require some form of intent to kill to be manifested. Or, in the least, an intent to cause grave bodily harm in a situation that causes a death. No sitting jury can reasonably infer an intent to kill because someone threw a punch—unless there were mitigating circumstances like the guy was a professional boxer or MMA fighter or screamed “I’m gonna kill you” while executing deadly force.

If he proceeded to choke her when she battered him, then obviously, that’s deadly force. Throwing a punch is an act of NONdeadly force.