1. The shine at the top middle doesn't look like it is a Nexus 4. Also, the curvature of the corners don't look right. The phone in the mug does not look like a Nexus 4 to me.
2. (And really the only evidence you need) There is an obvious cut. I downloaded the video and opened it in MPEG Streamclip (I was bored, ok?) and stepped through the video at the fall. Note the frame number towards the bottom of the window.
Starts out where the video fills the whole frame:
Then a cut to where the edges are black, very next frame:
Ok, not a major deal. But now lets look at the fall.
Right after he drops the phone, note that there are still black bars and we are at the first frame of 1 minute and 55 seconds:
The very next
frame, 1 minute 55 seconds and 1 frame into the video, hard to see but the black bars are gone (the thing that gives it away is the low bitrate on the video and it not being 100% black):
Now at this point, it is only 6 frames later and here you can see more clearly that the black bars are gone:
So the obvious cut in addition to the phone in the mug not looking like the Nexus 4 makes me think it is fake.