He wasn't convicted of intentionally murdering someone.
Murder 2 is an unintentional homicide, but brought out by an intentional assault.
Other than that, your overall point still stands. They all seem mutually exclusive.
Murder 2: Chauvin meant to assault Floyd, and Floyd unintentionally died as a result.
Murder 3: Chauvin was doing something dangerous, not necessarily directed at Floyd, and Floyd died as a result.
Manslaughter 2: Chauvin, through negligence, allowed the death of Floyd to occur.
They aren't actually mutually exclusive, at least not right now.
Murder 3 is:
Whoever, without intent to effect the death of any person, causes the death of another by perpetrating an act eminently dangerous to others and evincing a depraved mind, without regard for human life, is guilty of murder in the third degree and may be sentenced to imprisonment for not more than 25 years.
It used to be that 2nd and 3rd degree murder were considered mutually exclusive when only one specific person was the target of the perpetrators' use of force (i.e. the perpetrator put multiple people in eminent danger), but the Noor appeal verdict effectively overturned that precedent by reading "others" as 1
or more.
That's what fucked Chauvin. 3rd degree murder was initially thrown out by the Judge as he didn't think Noor set a precedent, but the appeals court said otherwise.
Since Minnesota doesn't have merger doctrine, he can be (and was) charged with both. (i.e. he was found to have both committed a felony and put 1 or more persons in eminent danger which resulted in a death). Likewise Manslaughter 2 isn't actually mutually exclusive either for the same reason.
For clarification, Manslaughter 2:
by the person's culpable negligence whereby the person creates an unreasonable risk, and consciously takes chances of causing death or great bodily harm to another;
In Minnesota culpable negligence means "acts that are grossly negligent combined with recklessness".
An act can be both eminently dangerous to others
and grossly negligent with recklessness and unreasonable (again, no merger doctrine. This would otherwise be a lesser included charge of murder 3).
The Noor decision is now playing out in the Supreme Court, and if they reverse the Noor decision then Chauvin will be able to successfully get the 3rd degree murder charge reversed. If it stands then he won't. It won't affect manslaughter 2.