It all depends, of course, on how you define a carol. Originally it was a circle dance, then the same done around a maypole. As such events were community events, the name attached itself to songs sung while doing the dance and eventually to songs sung at these special occasions. Even later, the term "Christmas carol"was defined as songs sung by carolling groups who went round an area at this time. It was the Victorian Middle Classes, who restricted the name to exclude all except religious songs and hymns, as power-hungry vicars stomped on anything lay-led in their parishes.
So, yes, "Swaledale" can legitimately be called a carol.

Pedantry over (for now!)

Chris B.