On the whole Fusen Ryu newaza thing:
My own personal belief (admittedly based on grappling experience, rather than historical research) is that that the focus and subsequent development of newaza is a function of the rules of competition, rather than an expression of codified techniques. In the famous Kodokan v. Fusen challenge match, it sounds like the Fusen competitors pulled guard and fought for a draw - a very sensible strategy when facing nagewaza experts, given that butt-scooting wasn't expressly forbidden.
Moreover, wrestling on the ground is good fun and a pretty safe way of developing conditioning and drilling principles and techniques. I can quite believe that while there may not be codified ground techniques in the Fusen or Daito Ryu syllabus, that practitioners wrestled informally for fun and tried to apply the techniques of their art. And I certainly believe that competitors studied the rules of potential challenges and their opponents' styles to come up with unorthodox strategies to beat them. You wouldn't need to be Rickson Gracie to be able to submit an opponent who had never trained on the ground (whether a western wrestler or a kodokan nagewaza expert) - all you would need is a game plan, and a modicum of technique. I'm not denigrating Tani et. al. here - just suggesting that they came to the west with a clear plan of attack.
"Handa" could well have been some kind of Fusen or Daito Ryu for all we know - to a western author of the time any techniques starting from kneeling would count as "starting on the mat", and a focus on kansetsu waza and pinning techniques would look more like catch-as-catch-can than the nagewaza of the Kodokan - especially in a randori situation.
Just my rambling, non-scholarly, layman's p.o.v.