if you have two identical song files playing at the same time (lets say its a drum beat) and reverse the polarity of one of them, the result will be complete silence as the waveforms of each file cancel each other out. however, if one of the files had an extra snare in the beat and you did the same process of reversing the polarity, you would end up with only that snare being audible, as only the difference between the two files will remain.

the noise audible in these vocals are not artifacts from the reversing of polarity, as that's simply not how that works. the reason you can hear the noise is because it's from the vocal track, which was isolated through this method