I asked our weaving teacher today about the puzzling scarf. Her suggestion is that it's probably made from two different yarns, even if they are both merino yarns. The puckering is definitely in the weft threads. So it's not like seersucker where different tensions are applied to sections of the warp. The areas which have shrunk down do have a felted appearance and there's a thread carried over between strips of weft which you can see at the selvedges--sorry, I didn't catch that in the pic.
I'm just going to go back and add the makers name to the tags on this morning's blog. Could I get lucky and hear from her?