About that link. Look at the last image. You will notice "Q" AF point during AI Servo AF. If you press the Q button you can select illuminted. The AF points that you or the system selects (zone) will illuminate when shooting in AI Servo.
If you previously set the VF dislpay to AUTO then this will only work in low light. If you shoot during the day and you want see the AF points in use illuminate, especially if you have the AF display points set to all 65, the red flashing AF points can help you see which points are active. Set the the VF display illumination ON instead of AUTO. Keep in mind this will probably drain the battery a little faster.
Also if you want to see which AF point/s activated while viewing the images on the LCD go to the blue menus >, the 3rd tab. Second menu down. AF point disp.