We had a bit of discussion about that mix when it started making the rounds:
http://www.u2wanderer.org/rtss/viewthread.php?tid=138I've heard three separate stories:
It's official, and it's an unreleased promo, 250 copies, etc. (Really doubt it.)
It's official, but it was shelved/deleted/etc because U2 Inc. were not impressed. (Possible.)
It's not official; it's just your typical, average 3rd-party remix. (My guess.)
I agree with the one poster in the thread I mentioned above; anybody who remixes a U2 song with any kind of official sanction would want their name associated with it, even if it turned out that U2 didn't end up using it (e.g. Ferry Corsten's original NYD mix, if I'm not mistaken).