Check the facts and think critically

Once I was at a conference and the speaker gave a strange analogy of how fast hard drives need to work. He said, "Reading of bits on the hard drive plate is like a fighter jet flying at MOCK-4 1 foot off the ground counting every grass blades on the ground.". Can this be true, can we calculate if he was correct or just exaggerating? How would you start designing this program?

By my calculations, for a 3.5inch hard drive, the outer edge is traveling at 78mph and the inner track at 33.45mph. MOCK-4 is a supersonic speed 3069mph. If I'm correct, he was WAAAAY off. Can you check my values?