I was quite confused during the race and after it about what actually happened. Reading the news from 3 different websites did not help as one reported Trulli to be saying and doing one thing while another reported the opposite. But after reading what Keith reported on F1Fanatic, I'm convinced of the truth. Here it is and I quote Keith:
"Meanwhile, unseen by the TV cameras, Trulli went off the track, losing what was now third place to Hamilton. Trulli then re-passed Hamilton after the safety car had arrived on track, and was later handed a 25-second penalty by the stewards which demoted him from third to 12th.
Trulli’s form at Melbourne was quite atypical: out-qualified by his much heavier team mate, but in superb form on race day, he deserved much more from the weekend. He later claimed Hamilton had slowed and he had no choice but to pass the McLaren.Hamilton inherited third place against all expectations, and was the highest-placed KERS-equipped finisher."
Source : F1Fanatic