it is fake, in the video all 4 instruments are next to the meter thing while there are only 3 instrument highways while there playing, just vocals, guitar, and Drums."
As with the false "FAILED" badge, the fourth instrument icon is just part of the dreamscape. Harmonix going all "meta" mixing and mashing the elements of the game upon itself in the same way the samples in the song wind around.
(Just in case anyone doesn't get it, yes, this is all just a little fun. The fake R#9 holds up just about [but not quite] long enough to be convincing for the seconds it is on screen.)