This is not legal jargon as far as I know. I don't know how the Flordia statutes define their levels of murder. Premeditated murder is a colloquial way of saying the actor intended to cause the death of the victim.
Now, who writes state laws? State legislators. Not always the sharpest tools in the shed, let alone great students of English. Perhaps that's what the statute calls a lesser degree of murder. Or perhaps it is just the way the police distinguished it from premeditated murder aka 1st degree murder and other names signifying the conscious intent of the offender was exactly what resulted from his act.
