It's a fingering/reading exercise (not theory), just take the notes as they are.
If you play the exercise you'll see the logic of the sequence, the notes go up and then down. The enphasis is getting your fingers in shape and to learn where the notes are.
The first part of the book is mostly about learning notes on the fretboard, reading and fingering exercises, but little to nothing about intervals, scales, etc. It's hard to make sense of these beginning exercises (and explaining them) without basic theory, which is a flaw of this method imo.
If you really want to understand what you are doing you need to learn a bit more of theory: intervals and the major scale.
Otherwise just obey the method blindly for the time being, until more is revealed.
There are tons of resources on the net, you can try this one:
http://www.studybass.com/lessons/bas...ical-alphabet/