Thanks for writing in. No, the device does not support video out. The Nexus 7 demo was done in conjunction with the Nexus Q.

That's a good theory.  However, that wouldn't explain how they showed a demo of the Google Maps "Compass View" feature.  Check out this part of the keynote that shows the feature:

Nexus Q is for streaming content from Google Play.  So how did they do that demo?  Also, you definitely can see that the tablet is wired during that demo.