As it is his good right, isn't it?
As stated above, a five course dinner is just the normal set up if one chooses just one of each of the sections per menu. It is even in the Cunard information available to everybody, "The five course evening menu changes daily and features...", thus everybody could know that this is what to expect.
To the OP: Do not worry, it is absolutely normal to have several courses. Also, the stewards are normally quite good in adjusting the way and timing of service such that, at least on a sociable table, different numbers of courses do not become an issue.