They did point out that he was a preexisting character in the 5th paragraph. They are just gathering enough power to become a stronger threat compared to prior encounters. Still, I wouldn't place them as a new strongest enemy when the list includes villains such as Nekron and Darkseid.

Toy Story 3 was a farewell to the characters many of us loved and grew up with. The fact that 4 exists at all is an insult to what could have been an excellent final goodbye. I would have been fine if they made a new series focusing on a unrelated group of toys experie cing their own story, but Disney is going to do Disney things and drag good things through the mud for the sake of profit.