Dude, were you even listening to it? There is no way those vocals were pre-recorded. You think Interscope would listen to that and let it fly? Fergie's mic was even muted for the first 10-15 seconds of the set. The mics cut out more than once. The vocals were completely dry, no reverb, nothing, except for some autotune on the one dude's voice for effect, and extremely to the front of the mix.
There were no backing vocals (which is what I meant by tracks, not the music) whatsoever and the music itself was so low it was barely audible.
I really think it was the artists' monitor mix that was sent out to broadcast instead of the actual mix, probably on purpose. You can't just "fuck that up" in my professional opinion. It sounded like someone doing really terrible, off key covers of Black Eyed Peas songs.