I think instead of trying to shoehorn the "AND" that he discusses in the article into a case statement you'd just look for each category to see if there has been a non expressed delivered package.

  SELECT 
      category, 
      ISNULL(NonExpress.NonExpress, 0) AS ever_been_non_express_delivered
  FROM @orders O
  OUTER APPLY (
     SELECT TOP 1 1 as [NonExpress]
     FROM @Orders O2
     WHERE O2.Category = O.Category
        AND express_delivered = 0
  ) NonExpress
  GROUP BY category

Edit: Changed the logic up, the original code's field was contradicting my logic.

How about:

  CASE WHEN MIN(express_delivered) = 0 THEN 0 ELSE 1 END AS always_been_express_delivered