A PB of 10.03 to an unbelievable 9.69 WR in a year is a lot of smoke.
Did you see the difference in technique before and after that year? Bolt was an absurdly quick 200m runner who occasionally ran 100m, and even as a 200m he still was technically raw.
Bolt was pretty quick as a kid despite of himself. He's so tall that he had almost no lateral stability, which is still a problem for him especially during the transition from the start phase. Whether he was on drugs or not in that year, his technique came on leaps and bounds. He still rocks and rolls but he's far more stable that he used to be, allowing him to fully extend his stride when driving.
I'll try to dig out the video, it used to be on youtube.
I'm normally the biggest cynic when it comes to dopers, but Bolt is so atypical in terms of body size, shape and composition that I'm willing to consider he just won the genetic lottery.
Carl Lewis was considered 'too tall' for a sprinter (normally between 5'9 and at a push 6'3) at 6'2 and 13 stone, Bolt is 6'5 and 12 stone. Doping or not, he's pretty unique in terms of technique etc.