Just means it wasn’t premeditated, and there’s no indication at this point that it was.
I don't believe it wasn't premeditated. The average person doesn't carry a knife large enough to do the job. The decision to bring one that big was premeditated.
As I understand it, the time period that defines premeditation can be as short as a few seconds -- just long enough for the perp to form "intent."
Hard to see how the perp's actions in this case don't meet that standard.