And what if "the intruder" was someone who wanted to kill you and your whole family? Many people in the US are acquitted of killing intruders or people they thought were intruders because of the finding they genuinely believed it. You can say it's a fact he did not believe it was an intruder but that's is not a fact. It's a belief and the only person who knows if this is true or not is OP. All of us, including the judge, looked at the facts, the evidence, and the believability of his story and some of us, most importantly the judge, decided that it is quite reasonable that he thought and intruder had entered his home. There's certainly no proof he didn't.
And as I said before, if the judge rejects the state's version, the benefit of the doubt goes to the defendant. That's what happened here.