In ATTI mode, the sensors do nothing, above 22 mph, the sensors also do nothing to avoid obstacles, if that is what you are referring to. ATTI has only a barometric sensor for navigation, it will attempt to hold altitude, but that is all. Without GPS data, it would not know how fast is was moving, there is no air speed sensor. In a slip, a plane will accelerate if no opposing input is made, this will result in a high speed slipping movement that can raise the speed significantly in a very short time.
One slight correction - the log file does contain x, y, z velocities even in ATTI with no position data, which the FC is, presumably, calculating by integrating the accelerometer data from the IMU.