It was absolutely a fumble. What you're missing is that the refs ruled that Washington recovered it. However, if you watch Duke Johnson (the HB), he comes out of the pile with the ball while the refs are still digging through the pile.
Here's another angle:
http://giphy.com/gifs/14sO4wqDNz4DUA
You can see the ball pop out there and bounce back towards Duke Johnson (HB). If you watch the video in the OP, you can see Duke Johnson pull himself out of the scrum and hold the ball in the air.