You guessed it. That string you saw is the only way for that. And when he yanked it back, the sticky holding the puck and string together came loose.
String is permanent to the stick. he used a sticky tip of the string on the puck. Thats why he used a very light shot to hit it the first time and a jerk motion to break the sticky and change its direction. then he shoots as normal. He can then remove the string while moving away and no ones the wiser.