Q19. Most productive actor

I submitted the answer below and it produces a different output from the correct solution.

Could someone please enlighten me about what exactly is wrong with my answer?

WITH film_actors AS (
  SELECT 
    first_name,
    last_name,
    film_id
  FROM
    actor
  INNER JOIN
    film_actor
  ON
    actor.actor_id = film_actor.actor_id
  ),
actors_film_count AS (
  SELECT
      first_name,
    last_name,
    COUNT(DISTINCT film_id) AS film_cnt
  FROM
    film_actors
  GROUP BY
      first_name,
    last_name  
  )
SELECT
  first_name,
  last_name
FROM
  actors_film_count
ORDER BY
  film_cnt DESC

LIMIT 1
;