This is the exact thing I've been thinking all the time: Something's not totally right here: Let's at least slow down to better assess the situation. Everything works better in slo-mo. My human brain would then have much better time to evaluate the scene. This would definitely also hold for the sensors and processing systems for an autonomous vehicle.
And even if it doesn't, and the system still concludes it's noise/an obstacle that isn't going to move etc., a low-speed collision is preferable to a high-speed one. Unless you can be completely confident you aren't going to hit something, slowing down is not a bad default action.