Sounds like you think it's an unusual curve, but it's not really. Once a post hits the front page it attracts the attention of users, or moderators, that might flag a post. Multiple flags demotes a post. Maybe because they don't think it's interesting enough, it has a clickbaity title, is ragebait, the discussion has descended into flame war, or for a variety of other reasons. The post then drops sharply. It happens fairly frequently, and might perhaps happen to this one too, because it could attract shallow, bordering on paranoid, discussions about the moderation of the site.