Jon, you're echoing Bert Lloyd's suspicions there, even though he set them out slightly more dramatically in'Folk Song in England':

[1967:] What ancient saga of trickery and revenge lurks behind the favourite joking song of Our goodman, Five nights drunk, The old farmer and his young wife? Known all over Europe, it tells of a man returning home to find another man's horse, sword, cloak, etc., where his own should be. Like an epic hero he asks in formula fashion: Whose horse is this? Whose sword? Whose cloak? Each time the adulterous wife insists that his eyes deceive him, and that the objects are really a cow, a spit, a bed-sheet, etc. In the ballad, the husband's rival appears only at the very end of the song and then merely as a head on the pillow. No struggle takes place, there is no retribution; the ribaldry of the situation has seemed sufficient for modern singers.

Yet somehow, in the form as well as the atmosphere of the song, there is the sense of something far more than a rough joke, something larger than life, something to suggest that important things have happened before the song begins, and that weighty and perhaps terrible events will occur after the song ends. In his studies of the medieval folk ballad, Lajos Vargyas makes a fleeting reference to Our goodman in connection with what seems on the surface to be a separate and distinct song, namely the ballad, known in Hungary as Barcasi, with parallels in the Balkans, France and Spain, of the couple surprised in adultery by the returning husband, who kills his rival, daubs his wife with pitch or gunpowder and burns her. In 1879, the Russian explorer Potanin found an epic version of this theme in north-western Mongolia, in The tale of Tonchi Mergan. But more research is needed before we may surely link our drunken cuckold to the mighty Mongol hero, or identify the strange head on the pillow as belonging to a foreign warrior, or declare that the cheating wife is the lineal descendant of that bygone adultress who was trampled to death by eighty mares on the steppes of Tannu Tuva. (Lloyd, England 147f)