Why is my answer "wrong"?: 110. Most popular product by category

My solution below was marked as "wrong", why?

SELECT product_category_id, product_id, ranking
FROM (
     SELECT p.product_category_id, o.product_id, sum(o.qty), 
     RANK() OVER(PARTITION BY product_category_id ORDER BY SUM(qty) DESC) AS ranking
     FROM orders o
    JOIN product_category p on o.product_id = p.product_id
     GROUP BY 1,2
) x
WHERE ranking = 1

Yet the solution is this:

WITH prod_cat_qty AS (    
    SELECT product_category_id, O.product_id, SUM(qty) AS quantities
    FROM orders O
    INNER JOIN product_category C
    ON C.product_id = O.product_id
    GROUP BY product_category_id, O.product_id
)

SELECT product_category_id, product_id, quantities, ranking
FROM (
    SELECT product_category_id, product_id, quantities, RANK() OVER(PARTITION BY product_category_id ORDER BY quantities DESC) as ranking
    FROM prod_cat_qty
) X
WHERE X.ranking=1

Both yielded the exact same output. Would my solution in an interview me looked as "wrong"?