Why don't you ask him if he wants to start a civil war, since you believe that's what he meant?
Well, you threw your hat in the ring and said he didn't mean it that way, which of course is total bullshit. Of course he meant it that way. Who says "you up for that?" for any other reason? I've never heard that phrase used in a context that wasn't inviting, daring.
Unlike you, I don't claim read other people's minds or say that I know their motivations based on insufficient evidence. I'd rather ask and confirm or refute your claim.
