Similar but still still different. Lots of 2nd degree murder cases get pleaded down to manslaughter for a myriad of reasons. Plenty of 1st degree murder charges get pleaded down to 2nd degree for a myriad of reasons.
Manslaughter requires provocation that would drive a reasonable person to go blind with rage and kill.
Example:
Murder and Manslaughter: Case Example 1
Facts: Fast Boyle is walking along a busy street. Clay bumps into Boyle and continues walking without saying, "Sorry." Angered by Clay's rudeness, Boyle immediately pulls out a gun and kills Clay.
Verdict: Boyle could probably be convicted of second degree murder, because he killed Clay intentionally. A judge or jury is unlikely to conclude that the killing was premeditated, which would elevate the shooting to first degree murder. On the other hand, this wasn’t the kind of heat-of-passion killing that equals voluntary manslaughter. While Boyle might have been provoked in some sense, the circumstances weren’t so extreme to cause a reasonable person to lose control.
Like this example, the John/Steve shooting was a killing without premeditation but with malice aforethought. The Scott shooting was also a non-premeditated killing with malice aforethought.