Nope. You've confused being wrong with being irrational. Also, your analogy is weak. Explorers have seen other landmasses, so a hidden landmass wouldn't be impossible. That's dissimilar from creating something from nothing or being a disembodied mind.

You're leaving out the pragmatic aspect of belief. We can afford to dismiss that which is outlandish, given the lack of solid evidence in theism's favour. True, atheists might end up mistaken, but that wouldn't imply they were irrational in wasting their time with apparent nonsense.