I think that definition is pretty good, but nonetheless is lacking something.
IMO, a neutral DM does have their thumb on the scale for the players, even if it is to a nearly unnoticeable degree. You see this in the common advice of telegraphing threats, which is a significant component of "skilled play". After all, there's nothing skilled about making an uninformed decision, any moreso than there is in a coin flip. Yet, telegraphing threats is favoring the players. It certainly doesn't guarantee success, but it guarantees that they have a chance.
It's kind of how the old Bond villains used to leave Bond strapped to a table, a laser aimed to bifurcate him within a minute's time, and then conveniently leave the room (giving him a chance to escape). The smart play, of course, would be to shoot Bond in the head while he's helpless (and then double-tap just to be sure). Of course, the latter approach, while certainly smart, arguably wouldn't make for a very good experience.
I see the neutral DM as more closely aligned with the classic Bond villain, rather than the "smart" Bond villain. The neutral DM gives the players a chance. If they fail to escape and the laser cuts them in half, the neutral DM certainly won't conjure a deus ex machina to save them, but they will have had a chance to avoid the outcome.