Three strings, an arched bow, and played on the knee? Could it have been a medieval rebec? Check out the Harvard Concise Dictionary of Music under Violin Family.

Another possibility is the Irish Box Fiddle, as described in Musical Instruments of the World (Bantam Books 1978). The diagram has four strings, but the homemade quality is stressed, including the description of the orange box body (shades of Bo Diddley).

I know of similar confusion with the instrument known both as the Cittern and/or English Guitar. Nothing like the Playford Cittern, and not used to my knowledge in English music. I'd prefer to call it a five course octave mandolin, or even a flat-backed bazouki, but I'd only be adding to the coufnsion.