It is Madara, but the thing is that it's him using a different body (Not exactly sure why as it hasn't been revealed yet). But this was pretty clear when you think about how the body is much younger than what would be a 100 something year old body, but also when Kabuto brought up coffins holding several bodies such as Itachi and Deidara, and then he showed Tobi a certain body that forced him into accepting Kabutos offer, which that certain body is believed to be Madaras real body.