The problem with naive occupancy grid mapping from sparse LIDAR data is that things like birds, falling leaves, pieces of paper of plastic bags flying in the wind can mark the grid occupied.
Emergency breaking for all these cases would be very dangerous. The same object must be scanned multiple times to get the idea if the object is something to be avoided.
Quite true -- but LIDAR has a very high refresh rate, and it's not hard to do better than naive grid mapping. This was a full height pedestrian plus bicycle, which would have multiple nice returns from a Velodyne HDL 64 at these distances.
Birds, plastic bags, cardboard boxes, small pieces of wood, and pieces of tires are perfectly good reasons to apply brakes and drive with caution to avoid.
Emergency breaking for all these cases would be very dangerous. The same object must be scanned multiple times to get the idea if the object is something to be avoided.