I think the judge was wrong to tell them deadly force is justified against one but not the others. They were acting as one. How is Dunn supposed to know which ones were a threat and which ones were not? Sounds like the judge wants him found guilty of something. More grounds for an appeal.
You are reading quite a bit into that. If the law says that self-defense must be applied separately to each count, isn't it the judge's responsibility to tell that to the jurors?
*I don't know what the relevant law(s) are, I'm just making the point that I don't see anything in the judge's answers to indicate any kind of bias.