Yes, I know what he meant; however, if he forgets what year the Viking Lander landed (haha!) that means he forgot what year he was born. He said that he was born the year before that event, and even if he had forgotten exactly what year that was, then he could make a reference to his birthday to figure out when that event took place.

And no, I will not say he “misremembered” it. He forgot it. Plane and simple.