It is NOT, nor has it ever BEEN down significantly in AH trading. What you saw was a late print. You can tell because the bid/ask don't change; if the bid/ask are near one level and a print goes through way below or way higher than that without the bid/ask changing, it's a non-event.
Am not sure but if a buyer wanted 20000 shares and put the order in then a lot of holders could have been stopped out in order to fill it. I try not to pay attention to after hours will sell my call a 92.50 if the stock hits 99 to 100.