
Unfortunately, it does not prove this at all. It only proves there was a second person involved in the thing - since I'm assuming David didn't tie his own hands behind the chair he was allegedly found sitting in - which could still leave the whole affair firmly in the realm of kinky sex play gone bad.
Sorry, but unless a murderer confesses, Carradine will be seen as having expired in a thoroughly weird, embarrassing and self-inflicted manner. And when people think of him ten years down the road, that's what they'll think about, not Kung Fu or Kill Bill or any of the rest of it. A great argument in favor of dying in as mundane a manner as possible.