It's a player. An extremely close look at the picture indicates the player is sneaking. That greatly conceals his username display. Also, I asked if it was on Pocket Edition because on Xbox and Pocket Edition, he's still there. For instance, my friend was showing me a world he had started on about a month ago. He lived in the Extreme Hills biome so he was climbing a cliff to show me a house his friend used on Multiplayer. When we got there, it was just a flat layer of fire with a nearby sign that said,"There were three dogs here. I killed them.". It was really scary.