An abnormal spike coupled with Typed/Bookmarked referrals (i.e. direct traffic) and also with unusually large bounce rate sounds suspiciously like bot traffic. If these are bots, then they wouldn't normally save any cookies, let alone Adobe's visitor ID cookie. As a result, every hit is essentially a "new" visit. And since bots also normally don't send any document.referrer data, AA would then classify them as Typed/Bookmarked referrals.