The thing is there's nothing particularly unusual about the story as such. Stuff like this happens pretty regularly in real life. (For example see this rather horrible storythat I came across today when looking for soemthing quite different, about a man who went out and killed his former lover and her family; he also beat a dog to death with a shovel. Typical ballad material, except he wasn't a lord. Unlike the equally unsavoury Lord Lucan, who could also have well featured in a ballad.)

I'd have thiught it pretty likely that the text we have does in fact relate to some actual episode, though it'd likely enough have incorporated stuff from some pre-existing account of the same kind of thing.