I think I understand why it's 2nd degree and not manslaughter in this particular case. If it were just manslaughter, there really was no crime. Manslaughter implies no ill will doesn't it? Here we had an altercation, one had a gun one did not. If...if there was a crime, it's more serious than manslaughter. I think that's why.
I am not adressing his guilt one way or the other here, only the reasons why it might be 2nd degree and not manslaughter. Then again, you never know, the judge may give the jury that option when he charges them.