Hi There,
Thanks for reaching out to Adobe Community.
As it says on the page " On currency event reports, the report total represents the de-duplicated event total (in this example, the total amount of discounts during the reporting period), not the sum of the event values for each product. For example, you would see "9.95" listed for both "Running Shoes" and "Running Socks", and the total would also be "9.95".
As per the doc, the total order had two items, hence event 21 was applied to the entire order but the discount amount was for the correct product.
Thanks!