Interesting but not quite the same thing. You can frequently lowpass music that has a lot of high freqency components and not notice the difference until the filter is set remarkably low, this does not mean you cannot hear those frequencies.
FWIW, I could ABX the 20.5 khz sample (lots of concentration and "let the force guide me", but repeatably 8/10 right). I don't remember the whole tone of the music, but the key element for me was the harmonics of some bells.
I got zip on the 21 khz sample.
After I was well used to those bells at various low pass, I could reliably tell the difference at 17 kHz in the ABX test while ONLY listening to the X sample.
To me that is the minimum standard if someone starts saying "The difference is obvious"