As for the vendor's numbers, they may or may not be completely correct, which doesn't mean their testing scenario matches your scenaro. I'd certainly believe the unit will not be quieter than their claimed numbers. Any skepticism should be in the other direction.
Let's try an analogy that's easier to see, pun intended:
You have a light that's emitting 1000 lumens. If you view it from 4m, how many lumens is the light emitting? If you said 1000, you're right! The bulb performs the same regardless of your distance from it. That's the POWER of the bulb, unaffected by the location of the observer. Now pull out your light sensor and see how bright it is at your 4m location. That's the EFFECT (loudness if you will) the bulb has on your location. Further, that result will be affected by environmental reflections. The bulb will illuminate better in a room painted white than a room painted black.