Yes, this is how it works, legally. If I shoot someone in self-defense, and someone else nearby mistakenly but honestly believes that I just murdered someone in cold blood and puts my life in peril trying to subdue me, I have a valid self-defense claim against them, too. 1/
If Person A and I are having an argument in my back yard and Person A pulls a gun on me and I shoot them, I've acted in self defense. If Person B comes around the corner and sees the dead body (but not the gun) and charges me with a knife, I can defend myself against them, too 2/
It's regrettable and terrible when these sorts of things happen which is one of the reasons I said repeatedly that it was a mistake for Rittenhouse to even be there. I would even not rule out charges for anyone who may have provided him with the gun and transportation there. 3/
That is a different question from whether Rittenhouse is guilty of murder. 4/