I am agree with you. I think before we examine the moral luck case, we also need to spell out an account of emotion as well(well, personally I think we need to do so in most ethical debate as well). A common intuition seems to be that emotion aroused when perceiving a circumstance is more or less, objective, rational and logical. Or, it is " because the circumstance i percieved is outrageous, therefore i feel angry" The moral luck case, if we have not clarified the role of emotion, seems to impress us this way: the circumstance of hurting the child IS outrageous, therefore the other FEELS anger. It causes us to believe that there is a paradox going on. So it is as if saying "oh my, how could both case that should have brought anger but people do not feel the same way? Illogical! Irrational!" But, lets say you adopt the "emotion as if perception" view(although not an all-the-way attractive view either), the anger felt by others can be like a mistake made by our perception mechanism(like the fake barn case), but not directly a mistake on personal level. In the similar way, that we felt anger might be because we naively percieve and judge based on only a few facts of the accident, but were we to find out that the doer was innocent or,say, distracted by a strange looking driver in the next lane(like realizing the fake barn is a sheep by walking up close to it), our perception of blameworthiness could have changed. Beside clarifying an account of emotion, in thought experiment like this, I like to first think about the relationshop between attributable and accountable or responsible(on personal level, for sure).There are lots of things that we would easily attribute some view to it but does not mean the target are responsible. A quick example is that we would normal say baseball player would chase the baseball in a way that minimized distance and angle(or you know what, i forgot all the details), but the baseball player might just thinking" chase the bloody baseball!". It is hardly possible that he is calculating all those maths in his head when chasing it. In the same vein, we would tend to attribute "cruel" to a unlucky "wrong" doer, but in fact he was not responsible for the action.

If what i have said above are fairly sound, then the moral luck problem can be interpreted as not just a "luck" problem, but an epistemic problem concerning how much information we should have collected before we can justify or, not to over-intellectualize the mind, be confident of our emotion toward cases like the video mentioned.