I suspect there's a big problem in the other direction, too. If the system starts to brake every time it thinks it might need to, it will happen all the time. It might see false positives like this all the time and that's why it doesn't act on them right away.
If it's (appropriately) conservative about starting to brake it will be braking/slowing all the time. If it's not conservative, people or cars will occasionally get hit. The former could make people uncomfortable or carsick or create some subtler danger by stopping short needlessly. The latter might mostly work and mostly not kill people, except for when it does.