I'm not so sure...
Brawn is obviously in the know... and he's a man who generally doesn't speak crap, whereas Rossi has a bit of a habit of playing down what he's going to do next... e.g. extending his Yamaha contract, a 2nd test with Ferrari etc.
Either way, Rossi is going to need to test heavily before he's put in a race seat, because his bike fitness won't get him anywhere in an F1 car. So if he does test heavily for the Scuderia next season, I'd say it's a banker that he'll make the switch, if not... 🙁