The "tests" as demonstrated on the video, with a person holding the tuning fork in their hand, simply demonstrates how easy it is to produce a set of figures that "look good" without actually proving anything.
Demonstrate an unstrung guitar, not with the strings "muffled", "detuned" or "dampened", and with the tuning fork held in a freely hinged bracket, so EXACTLY the same downward force is applied to the saddle by the fork ... then energise the fork in EXACTLY the same manner, not just by flicking it with a fingernail, and you'll have some comparable results. What these results "prove" will be open to interpretation, but at least they'll be a reasonably direct comparison ... until then, just smoke and mirrors!!