"First" does not mean "exclusively". But detection of an impending obstacle should not start with classifying that obstacle. You need only know that some geometry that looks larger than trivial is moving at a vector that will impeded your stopping distance requirement. Until that is proven to work, it is pointless to try to "understand" the object or its intent.

I'll go further. To avoid clearings, ponds, and pedestrians, Self-driving cars should be highway-daytime only until proven reliable. Starting with the edge cases and building back to the easy ones is ridiculous engineering policy.