I'm quite sure it was running on PC. Tim Willits has said in the past that the Xbox version wouldn't be started on until the PC version is done. Moreover, id and M$ were negotiating a deal in the weeks up to E3. No way, id could've got it running on Xbox in such a short time. And what would the point be anyway? It wasn't playable.
Plus, it looked like it was being controlled with a mouse and keyboard.