It has been one of the most unusual classical music stories in recent memory. A commission from a large number of orchestras was the catalyst for “Sidereus,’’ an overture by Osvaldo Golijov, not only a local star but one of the most admired composers of the last decade. Yet questions about the creative process behind the piece - which is on the Longwood Symphony Orchestra’s Saturday program - have given rise to what is either a scandal or a tempest in a teapot, depending on your view.