There is an explanation. On heavily shorted stocks the shorts will buy into the stock as it ascends. Then on any event, such as earnings, they dump their shares to cause a scare. I have seen this many times and the stock recovers but the shorts are able to grab up a bunch of shares on their attack day. I have seen this work many times, even on good earnings. Buy the dips.
I will also mention, I have seen this plan falter if a few upgrades are announced on the day of the dump. Then you have a huge jerk up after the morning dump.