Well, this was unexpected. Kudos to mad.max, who pointed out a link to a MacWeek article reporting that Bungie's Jason Jones was on hand in Paris to present a Halo demo during the Paris MacWorld Keynote.
At the moment, nobody is really sure if this was the same demo, or something new... stay tuned as reports come in. If it is indeed the new demo, then there will certainly be a lot of them.
- Forum: Paris Expo - Halo demo