The IS-F (in the GT window) isn't actually driven in the game. It's reproducing the actual drive (by driver Juichi Wakisaka) on the real Fuji track. Basically the video is showcasing how the data logging is being reproduced by the game.
Here's quick translation from the page:
CAN (Controller Area Network) exports to USB memory card and that information is loaded into a simulation engine of "Gran Turismo" and shown as a video replay. You can also play as a ghost and can also help you analyze your driving.
CAN (Controller Area Network) logs information about G Force handling, brake and accelerator operations, and includes rotational speed of each wheel and engine speed allowing a highly accurate reproduction of both the vehicle and location information.
Other the the N3 instead of S1, the physics and car handling in Prologue is quite different than the one in GT5 (proper) as the TT has shown. I can imagine the second half of Fuji where all the corners are will take a bit more effort in GT5 than they do in Prologue.