Relatives and friends in Georgia. They use Calvary for both the mount and mounted soldiers. I think this usage goes quite a ways back; how the confusion started, I don't know.
My feeling is like Dave Bryant's, I thought the term Fiddlers' Green is old, but I can't find any references.
Mention of Dana's "Two Years...." made me check his "Dictionary of Sea Terms" but all I found was "Fiddlehead," the carving at the prow of a ship if it bends in, in a curve like the head of a fiddle.
Not in Lever's "Dictionary of Sea Terms" either.