The simple answer is Worsley is using all of the techniques, in combination, for all of the parts!
To be able to analyze a work like this you need to know how each of the mediums are used, ie. the various ways they are applied, how they behave when applied and how they interact with each other.
- Crayon makes a variety of marks; broader than a pen-stroke; sensitive
to pressure; shows texture of paper.
- Pen uses ink and makes a hard edged stroke of different weights; ink is liquid so it will diffuse in wet areas, be sharp in others, can be brushed for washes, etc...
- Gouache is opaque watercolor and is applied by brush; used to make areas of solid and blended colors as well and sharp details; will also diffuse in wet areas.
Experiment with the different mediums cited, both on their own and in combination, to understand what is going on in the artworks and then you can reproduce that style. All of the techniques here have extensive documentation in print and online to get you started.