I don't know. "Imma bag myself a negro today" sounds like premeditation, in that you've made the decision to go kill someone. Which would be first degree.
For second, I think the argument they were trying to make was that Chauvin was using excessive force which resulted in George Foreman's death.
For third, they were arguing that applying the neon neck was inherently dangerous and the way Chauvin was acting showed a depraved heart.
You can read the actual statutes for
Second and
Third, specifically for Minnesota. Laws can vary state to state. In California, far as I can tell, 2nd degree murder is similar to what you have, the deliberate killing or someone but without premeditation. California also doesn't have third degree murder.
Confused? Welcome to the US justice system!