That's not the point. There is no "measure OR listen" scenario to begin with. We can do both just fine and see the correlation. Ear listening may also be perfectly right... Or sometimes heavily fooled. In that case, the "experiment" is just flawed :
"Let see if this can make a difference" (deliberately ignoring that he and his friends already believe it will), then,
"How surprising, it does indeed make HUGE difference". That's confirmation bias 100%. Only a blind test would be valid in that case. Obviously "huge difference" in sound should be seen by measurements. Otherwise, some believe in magic.
That goes without saying...