I assume you couldn't watch the video because it's just a live stream of a guy standing in a kitchen and talking to his glasses. He's not on the stage with hundreds of people on the wifi and you can't see what the glasses are displaying at all.

The link in this thread to the live glasses live demo is of Zuckerberg at FB Connect. The "fail" is when someone repeatedly tries to call the glasses he is wearing on stage. The person calling apparently has no trouble making the in-bound calls but the glasses Zuckerberg is wearing on stage fail in successfully answering the call. And the streamed video clearly shows the interface of Zuckerberg's glasses full-screen, as well as showing that the interface is being sent to the stage screen so the live audience can see it.

So, the failure was apparently with the glasses Zuckerberg's wearing on stage not establishing a two-way video call while simultaneously streaming it's own interface for the live stream and big-screen. He said it worked dozens of times in rehearsal and one notable difference was that for the real demo hundreds of other wifi devices present in the room.

I have quite a bit of experience producing live keynote demos at large tech events, so I don't think I've confused about this. As an aside, when we're being shown "Zuckerberg's POV" through the glasses I believe that's actually something custom put together for demos because the normal glasses don't even have a mode which shows the wearer's POV. Creating that view requires sending both the internal output of the glasses, which is the corner inset overlay AND the full screen output of the glasses live camera - which are then being composited together backstage to create the combined image we see representing what Zuckerberg sees. Sending all of that while establishing a two-way video call is a lot for a resource constrained mobile device.