Well, they have to talk with the actors early enough for scheduling - but a season is not green-lighted before the Network says it is. Happens with Sherlock all the time, there is always someone accidentally confirming early that the plans are already in motion, but as long as the network doesn't confirm, nothing is set in stone. So I hope that WG happened to speak too soon, but there at least already plans for more. Which is a good sign.