I think you're mistaking the definition of unintentional. This officer very intentionally killed the airman. When he drew his weapon and began firing, as you stated, he was firing to neutralize the threat. And for the police, you shoot to kill, not injure. Center mass or head. He intentionally drew his weapon and intentionally fired it until the target, intentionally selected, was neutralized, which includes the reasonable assumption of death.
Unintentional homicide would be like what Alec Baldwin did. He had absolutely no intent to kill that woman, but his negligence in handling the firearm resulted in it.
Read the paragraph on second-degree murder again (I somehow screwed it up in the quoted block). "... Leads one person to make an intentional decision to kill the other person. It was not premeditated, but it was intentional nonetheless."