It is a mark of unsophistication in music to pay no attention to the arrangement. That would be me, generally. I think of a song as the tune and the lyrics, the rest fairly optional. I do at least know this is quite wrong. I suppose this approach to arranging is similar to the old military saying that amateurs discuss tactics, professionals discuss logistics.
Yet sometimes even I notice things. I put this song up on a family text thread when discussing camping vacations from 25-40 years ago. (We were trying to remember what our nickname was for a particular camping food.) I did notice, as I had before, that it used unusual instruments for a 60s pop song. My wife commented on the films in the background, finding them inappropriate for the song. "I always thought it was more Eastern European. Those old scenes look English." Well, Hopkin was British - Welsh, I believe - and probably no one worked too hard to be authentic. But I agreed. "I always thought it was sort of klezmer. It sounds more Greek or Russian." I think someone told me it was a gypsy song years ago. Klezmer and Cigane were two styles that had enormous mutual influence.
So I listened more closely this time. A clarinet, a cimbalom, a balalaika, something oompah sounding which contributes greatly to the air of forced gaiety - I kept expecting an accordion or derivative.
I looked it up. The song was originally Russian with somewhat similar lyrics, had been sung by a gypsy, was in a British movie in 1953 with new English lyrics, and had been arranged in 1968 by someone more familiar with jazz than pop. Hopkin was only 17 at the time.