Maybe Reiza "cleaned the tracks" (i.e., redone them) in order to get the "dynamic track" feature in place. I remember that dust, Tarumã had it in some places too, but for me it was wrong. It was like that piece of tarmac behave like offroad in regard the dust - which seems a little bit excessive.
EDIT: giving a second thought, it would be nice if they put *some* (little) dust off-path on tarmac. Sure it would be a nice touch.