I'm not terribly familiar with Quora's UI, but it looked like that's the date that the person's author profile was last updated, not the date that they answered the question. I could be totally wrong on this though. It's not possible for the good answer to have arrived later, because the bad answer references it (unless he edited the post afterwards to refer to it, but if the date on the post is actually a last-edit date for the post, that still wouldn't make sense).