Well if it's using optical recognition then lower contrast or smaller object will always make the job more difficult then a bigger object with more contrast; then the reason why the model is better at recognizing white adult people. Even if the car is never going to strike a child or a black person the model recognition would still be better with them.
Pretty sure they are discussing 3-band cameras between 400nm and 700nm (roughly). If we start adding multi-spectral or hyper-spectral cameras to the mix then you'd have a lot more information to use, but then you'd have a lost more information to process.
Yes but by "bias" they just mean the miss rate is different. Digging into the study, they talk about visibility and contrast, and checked whether the problem is worse at night (which it is). They don't appear to be suggesting that the algorithms are prejudiced against darker-skinned people.