Weaving Puzzle

Here's a puzzle from the Scarf Festival.

I love this textured scarf: I tried to imagine how it was made and looked for more information on the swing tag: The only technique I can think of that would produce that sort of puckering involves using different yarns in the weft. If one yarn shrinks significantly when washed--or fulled--and the other doesn't, then the areas that don't shrink would be gathered in. The swing tag only tells me "superfine merino wool". That leaves me with a few possibilities to puzzle over:

• was the same wool spun in different ways in the different strips of weft?
• is there another fibre involved that hasn't been listed?
• or is there a technique that fulls and shrinks some areas while leaving othere areas untouched?

It's not quite keeping me awake at night, but I am intrigued. Suggestions please!