I've had many a brain freeze in my day, but I've never fainted because of one. If this guy blacked out after the brain freeze he got from a Slurpee, it makes you wonder how he managed to suck down enough of it to trigger such a massive reaction.
Unfortunately for four other people, the guy in question was driving at the time, and after he lost consciousness, his truck jumped the curb and plowed into a car in a parking lot with enough force to carry both vehicles into three others. (Check out the photos of the aftermath here.)
The guy did pass a field sobriety test, which leaves us with the possbility that you can actually black out from a brain freeze.
I did a little digging, and there's been some actual scientific research into brain freezes that shows they happen because blood vessels widen in response to the cold. The added blood flow helps the brain buffer against the effects of cold. (This is what gives you the classic "OH MY GOD, JUST LET ME MASSAGE THE BACK OF MY EYEBALLS" feeling).
There was nothing I could find that confirmed whether or not you can faint because of a brain freeze, although I'd imagine it might be possible from the shock of the pain of a really sudden brain freeze. If that's the case, then we're left with telling the guy who can't handle his Slurpees that he's a pansy.