That is very clever, but the article says that this drone "introduce[s] control surfaces into the airstream to change the direction of the airflow and create a

That is very clever, but the article says that this drone "introduce[s] control surfaces into the airstream to change the direction of the airflow and create a thrust vectoring effect." My guess is tiny spoilers around the inside of the duct to cause separation of the flow in one quadrant of the duct, allowing the Coanda effect to draw the stream in the opposite direction.