Well, the Psychological explanation is that we have two brain hemispheres: The right brain, and the left brain, that although connected, have a certain level of independence. Those de ja vu moments are a period of lag within our perception, where one side of our brain perceives something, but the other side takes just a few milliseconds longer, So finally when our whole brains perceive whatever it is we're perceiving it seems we have already experienced it before, but in reality it was just brain-lag
But I just like to believe I have ESP