Maybe, but not necessarily. It's not uncommon to have related fields in other tables as you no doubt know, but sometimes there are pairs (or even more). In a situation like I allude to, I can't recall if I thought the db was normalized to the nth degree, but I do know that the designers of the multi-million dollar system were IS professionals and I was not. These people seemed content to create many composite primary fields in this huge db, where others say no, create only composite indexes. Anyway, multiple inner joins between a pair of many to many tables did cause some duplication. I can't recall if the solution was to query that query or modify the joins.
Besides all that, if I understand correctly, he has some customers with multiple orders in a day. This must be a common situation in business, so that would make multiple order records for a customer a distinct possibility, correct?