No first person killed was an innocent elf. And the innocent human woman was killed in a misunderstanding. So the elves killing an innocent human by accident counts as the "true" reason for the start of the war but the humans killing an innocent elf on purpose is somehow arbitrarily considered irrelevant? Do only human lives matter? You seem to believe everything else about that codex entry, but the one thing you decide to declare unreliable is the part that would make the humans seem less like passive victims?
The elves weren't invading. Do you have a source for the claim that Red Crossing was later destroyed? I'm pretty sure that whole codex was describing the supposed raid on Red Crossing which he Chantry later embellished with false claims about blood magic sacrifice.
Siona's sister was killed before the event of Red Crossing, her death played no part at those event, and the elves didnt even had proof it was a human who killed her.
Misunderstanding? They killed her in cold blood, didnt even have her a warning shoot. And later killed more innocents who tried to protect their home against a foreign invaders. I have no doubt that humans killed elves too, but the ones at Red Crossing were innocents.
So when the elves invaded Orlais they passed through Red Crossing and spared everyone?