Not reall entirely a downforce issue, because 120 mph wouldn't give enough force to push a car on its side like that I think. I can recall many invisible walls like that which create a lot of friction and are "sticky", allowing the car to drive up them for a while. This is even with cars that don't have downforce. Because if you look in the Forces view, the large blue bars down the middle of the car is the downforce. They pretty much decrease as it rides up.
The real problem here though is Nick Heidfeld driving a Ferrari, :wtf2:
uhem... sorry to correct you, but it is the top of the tunnel. On a wall the downforce acts sideways, but the gravity still works downwards. Try it if you want
Depends how much grip the wall has. F1 tyres on tarmac hav a mu > 1 which would work. So it's not just any old invisible wall, it's a high-grip invisible wall.