I'm pretty sure imdb just hasn't been updated yet. Disney did create a unit that was going to work on sequels, I believe specifically sequels to Pixar films. The group was called "Circle 7" and the films were to be made without Pixar's input or involvement.
Then Disney bought Pixar and put Catmull (A Pixar guy) in charge of Disney Feature Animation, and also put Lasseter in a prominent, if somewhat vague position. As ryley26 said, Lasseter did say that TS3 would only be made if there was a strong story. A bit later (March), the Circle 7 group was disbanded, and work on TS3 stopped.
So unless they found that great story and restarted the work without telling anyone, its a dead project, or its at least comatose.