Sorry, but this is bad "science".
Too many variables, not the least of which is: strings, wood, pickups, scale length, frets, bridges. Not to mention these are guitars and not basses (different frequency ranges, different string masses, etc). To make a comparison like this valid, one would have to have three identical guitars, except for the neck joint. Same strings, same pickups, made from the same pieces of wood (not just species, but actual pieces), same hardware, etc.
I'm sure some people will look right past these basic insufficiencies and accuse me of holding on to unsupported claims, but I'm not saying that a neck-through has more sustain than a bolt on (I've never said that). I'm simply saying this so called "test" design wouldn't pass a basic first-year engineering class.