I have seen this happen before in small companies.
Once it was because of a snafu on scheduling the release with the Pres release distribution service before the market opened and the company put the PR out to its list thinking that it was after market hours and the PR would be out before the market opened. Not to give anyone an advantage---it was a mistake. Then the investors who had signed up for the e-mail list only got the PR to their box after it went out. Little company. Little problem.
Now if it was Home Depot, somebody would be in trouble. SO, who really knows? But it sure does not look like it was malicious.
And I agree with the poster who said it would be different if the stock was at its high of the day an not looking back. There was no guarantees how the market would react to this news.
Personally, I would like to see another states worth of Walmarts. Or a Costco sign on.