Cino posted in the HBO forum that a Bungie representative showed up there and showed the Halo 2 trailer. And guess what? It turned out to be true, as Matt Soell confirmed:

This is one of those weird times when something written about us on the internet is true.

I did actually show up in Renton with a DVD of the Halo 2 trailer, which I played between tournament rounds. It was on a tiny screen, and the glorious sound design suffered from the two tiny TV speakers, but it was the Halo 2 trailer, and people seemed to like it.

Looks like the rest of us will still have to wait a few days...