I Tivo'd the race and watched this section in slo-motion over and over. It became clear to me that Pedrosa caused this problem by slicing across the whole field from far outside to the apex, chopping everyone off. Rossi had nowhere to go, and had to dodge outside, forcing de Puniet out. I didn't see any contact between Rossi and de Puniet, but Randy avoided colliding with Rossi, only to collide instead with Gibernau, wrecking and sending Sete into the gravel.
Don't see any other options for Rossi, given Pedrosa's move. The Rossi haters will no doubt disagree with me, but I suggest you watch it again, if you can.