Excellent observation! It is indeed functioning as an approach tone. When writing the book I decided to leave the same interval name on any instances where a note functioning as an extension appears again within the same measure as an approach. I did this for the sake of making the sight reading of the interval script easier in these cases.
In other words, its like when you notate the 6 in a measure with a C6 chord and then in the same measure you notate the bb7 for a Cdim7. To make things easier for sightreading in both instances, the 6 and bb7, are notated with an “A” instead of “A” and then “Bbb” which is the proper notation. This has become common practice.
Hope this is clear and doesn’t instead complicate things! 🙂