I don't know--I actually thought it made sense that he didn't notice much about the blue car because his attention was pre-engaged with the side view of the 4WD. I imagine that watching the 4WD as it passed he looked away from the corner, and had less time to notice the blue car.Interesting thoughts. Confusion over who was in which car? Brought about by the huge delay in any official report?
Mr Chapman did seem to be more concerned about hoon driving and an unsafe child. And I agree that his view of the person driving the 4WD was much quicker/shorter than his view might have been of the driver in the following car, according to the walkthrough video.
He apparently only saw the driver for a mere second or two before focusing on the child in the back, then refocusing on the blue car as it came around the corner.
I think perhaps he exaggerated both the proximity to the other and the speed of the blue car; it was driving faster and more carelessly than he thought it ought to have been, he thought "and there's another one right after" because he was grumpy about so many hoons, and afterwards remembered them as being together when perhaps there wasn't much to link them really.
I wondered whether he originally did read the time as 9:50 and afterwards assumed he'd misread the clock, seeing that he believed the child was William and William was supposed to have disappeared at 10:30.