^The point Stardate
was making is that they shouldn't
have mistaken Ceti Alpha V for the lifeless Ceti Alpha VI in the first place, because it's implausible that an inhabited, Earthlike planet could be so thoroughly stripped of life by a planetary disaster. Even in the worst mass extinctions in Earth's history, life has survived, and the oceans have survived.
Not to mention that Ceti Alpha V clearly still had an oxygen atmosphere, since the robes Khan and his people wore outside were hardly airtight or pressurized. And anyone who knows the first thing about atmospheric chemistry knows that molecular oxygen is too reactive to remain present in a planet's atmosphere for long unless there's something to replenish it, and the only known thing that can do that is life. An oxygen atmosphere is a dead giveaway that a planet is inhabited. So there's no way in hell they could've mistaken Ceti Alpha V for another, totally lifeless planet. It never should've even been a candidate.