The Canon "auto fill flash" feature is a function of the camera body, not the flash itself. The camera senses the overall light level of the scene and if it is bright (like outdoors in sunshine) the camera reduces the flash power to so it will "fill" in the shadows.

This feature can be disabled via a custom function in the camera. I usually disable the auto fill flash function, since I never know how much the flash power is being reduced. When I shoot with flash outdoors, I just drop the flash power about 1 stop to start and adjust as needed.