Even if it were true that Steven is always right (not so, as mentioned by the others), that wouldn't be protagonist-centred morality - that would be an intelligent and moral protagonist (possibly one that's boring, but that's a whole different criticism).

Protagonist-centred morality is when what the protagonist does is right, simply because it's what they did. To keep this to SU, let's use the Sadie/Lars example others have brought up - if Steven's meddling had worked, or if Sadie and Lars's reaction was treated by the narrative as incorrect, rather than how Steven learns his lesson...that would be protagonist-centred morality.