It's also possible it was something blocking or confusing the camera system used by the safety system. The lane keep systems use a combination of radar and cameras to perceive vehicles/environment and lane lines.Happened to me the other day. It was snowing and the car had the cruise with LFA engaged. So it's not the same thing as outright emergency braking, but the car went from 40 to 20 in a second or two like it got cut off by something in front of it even though there was nothing there. Not under/overpass, just regular road. I attributed it to the snow possibly blocking a sensor or radar momentarily.