My best guess is the transformer winding is being used as an inductor, probably in a bass-cut control. Sort of rare in the modern day, but Gibson had bass cut switches in some 70's-80's guitars. And Guild's Starfire basses, a bass cut switch there as well. What's old is new again.
FWIW it is handy when using deep overdrive & many fuzz circuits, to cut bass from the instrument otherwise the tone turns to mush.