Yeah, whoever made the video was a modder. Modders are people who put 'Mod Chips' in their Xbox (or ps2, Gamecube, 360, whatever), which allow them to create or download programs that alter the defaults in a specific game. for example, they can increase the speed of the fan in Zanzibar, make Warthogs pink, or even have the SMG fire rockets.
In that vid (and several others like it), the modder detatched the camera from it's normal position and flew it back into the Longsword Jet.
Bungie no doubt had the Helet-under-helmet for just such an occasion.