> If it was an intentional pre-meditated murder

From what I understand he was convicted for second degree murder, specifically "unintentional second-degree murder while attempting to commit felony assault". So he may not have intended for George Floyd to die, but he did intentionally assault George Floyd who died as a result. So that's not intentional premeditated murder, but it's nevertheless a form of murder.

(He was also simultaneously convicted for third-degree murder, and second-degree manslaughter, but not first-degree murder.)