"These dates are by no means finalized, and are working dates that are most likely going to change," Daeke, of the studio's online community team, wrote on the game's official boards. "I'm not sure why this information was posted, but we will post the dates for things like Open Beta as we set them."
Update: VG247, which was among the initial sites to report the date, has explained that the information came from European publisher Namco. Apparently, the details were meant for the press, not the public, though that bit wasn't mentioned in the initial e-mail.
When I first read about the open beta I assumed it was an announcement from Cryptic... sucks that it will probably change, but understandable since the "news" was just a leak to begin with.