If LOST had not made it through Season 1 and was cancelled, it was the writer's easy way out to make all of this going on inside of Walt's head, which is why the polar bear page is in the comic book at all.
Benjamin Linus: Let me put it so you'll understand. Picture a box. You know something about boxes, don't you John? What if I told you that, somewhere on this Island, there is a very large box and whatever you imagined, whatever you wanted to be in it when you opened that box, there it would be? What would you say about that, John?
It might be that, in a previous iteration of the universe, Walt found the comic book with the polar bear, but because he's "special" (perhaps because Jacob selected him?) the universe actually reformatted itself to be consistent with his vision of a polar bear, and the Dharma Initiative's decision to experiment on polar bears is in some way "meta-caused" by Walt's use of his powers in the previous universe. Maybe that's how all the weird stuff that Walt does happens.