I realized that there may be an error with either the question, or the answer of a particular exercise in the SELECT tutorial under the lesson "HAVING clause" and the error lies within the "HAVING" part.
Link: http://www.sqlcourse2.com/having.html
Table link: http://www.sqlcourse2.com/items_ordered.html

3. How many orders did each customer make? Use the items_ordered table. Select the customerid, number of orders they made, and the sum of their orders if they purchased more than 1 item.

Answer: http://www.sqlcourse2.com/having_answers.html
SELECT customerid, count(customerid), sum(price)
FROM items_ordered
GROUP BY customerid
HAVING count(customerid) > 1;

The condition stated is "purchased more than 1 item", therefore, shouldn't the HAVING clause be:
"HAVING sum(quantity) > 1"
instead of
"HAVING count(customerid) > 1"?

If it were to be "HAVING count(customerid) > 1",
the question will have to read "if they made more than 1 order" rather than "if they purchased more than 1 item".

Both commands will return the exact same results because all the customers who purchased more than 1 item had made at least 2 orders.
However, if there is a case where a customer only made 1 order but purchase more than 1 quantity of a particular item, then the results will be different and hence erroneous.

Please let me know what do you think about this.