What people usually mean by "blues scale" is the scale that you already knew, i.e. a minor pentatonic scale with an added b5 ("blue note"). What the author of that book refers to as blues scale is actually more like a collection of notes, all of which can be used over a blues progression. The difference with the standard blues scale is that not all of those notes will sound equally good over all three basic chords of the progression (I7, IV7, V7).
With the standard blues scale, even though some notes are pretty dissonant over some chords, none of them sounds really wrong to our ears in a blues context. Even the b5 can always be played as a passing tone. However, the other scale contains notes that would sound really wrong (if played as target notes) over certain chords. E.g. the note E simply sounds wrong over the IV7 chord (F7) because it clashes with the b7 of that chord (Eb), and not in a bluesy way but in a bad way.
There are two ways how you can understand that collection of notes referred to as "blues scale" by the author. It can be seen as the union of the notes of the standard blues scale and the notes of the major pentatonic scale:
blues scale: C Eb F Gb G Bb
major pentatonic: C D E G A
=> C D Eb E F Gb G A Bb
Equivalently, you can arrive at those notes by filling up the C mixolydian scale with the two blue notes from the blues scale (the b3 and the b5):
C mixolydian: C D E F G A Bb + Eb Gb => C D Eb E F Gb G A Bb
Again, I wouldn't actually call those notes a scale, because there is no chord over which you can really play that scale. They are rather a collection of notes all of which can be useful at a certain moment in a blues progression. But then you could as well write down the chromatic scale and call it a blues scale, because if you know how to, you can play all 12 notes and make them sound good over a blues progression.
To answer your question about the major 6th, the A in the case of C major: it is not only a passing tone, it actually can be used over all 3 chords. Over the one it is a 13, over the IV it is the 3rd, and over the V it is the 9th. One way to use it, is to distinguish the I from the IV in your solo: you could play some motif over the I containing a Bb (and no E, because this won't work over the IV). Then you repeat that motive over the IV chord, but you exchange the Bb for the A. In this way you make the transition from I to IV very clear. But that's not the only use of the major 6th, because - as mentioned before - it is a valid tension for both I and V chords as well. One example: Larry Carlton start his solo over BP blues on the major 6th (he bends to it from the 5). Check it out here.