It probably does by phase cancellation, where they invert the left channel and then anything that is panned in the center (often the vocals) is cancelled out. That tends to also do away with the kick and bass. If they use a notch filter, any other instruments that have the same frequency as vocals will get killed too (piano, guitar, synths).
Probably, they perform the phase cancellation in combination with a bandpass filter to that only the vocal range frequencies get the phase cancellation. Depending on the mix, it might be effective. I would be VERY surprised if it worked as intended on most material...
-=bumpus=-