This image isn’t supposed to be about showing anything new. It’s supposed to be “I’m so excited. I’m gonna get a jump on this and download it so I can just install the patch on Tuesday!”

To answer your question: Blizzard has discussed this on multiple occasions. The Draenor visited in Warlords is an alternate timeline Draenor, not the same one from our present timeline. In a universe (or multiverse, rather) with alternate timelines, the butterfly effect cannot happen.