It's a rumour, and not officially confirmed (though Jay's tweet might be seen as confirmation), and I would not take this for granted until an official statement from Blizzard themselves (which will be very soon - possibly monday).
It seems kind of legit.
The fact they haven't openly denied it is a good thing and are also aware that we are aware of it. I'm not sure if that will wind up being the exact date, but it at least gives us a good date to estimate around.