Posting answers from GPT-4 etc on their own isn't interesting - they become interesting if you do the extra work to verify them first.

Because it’s a (worse) variant of one of the first queries the article gives:

  SELECT *, COUNT(*) 
    FROM t1
   GROUP BY x, y, z, ... -- all attributes of t1

  EXCEPT

  SELECT *, COUNT(*) 
    FROM t2
   GROUP BY x, y, z, ... -- all attributes of t2

and we aren’t discussing ChatGPT here.