Unicorn points are a myth.
He got the try assist because he kicked the football. There is zero grey-area with that one, if you kick the ball and a try results from that kick, you get a try assist. On rare occasions they'll sometimes even give 2 try assists for a try resulting from a kick, if the ball is regathered cleanly by another player and passed on to someone else. An example of this is the Clint Gutherson try in Round 6. Mitchell Moses & Dylan Brown were both awarded try assists for that try.