Fel Reavers are gigantinormous demonic machine denizens of the Hellfire Peninsula...which is in Outland. Here's the terrible twist: Omgcookies from the World of Warcraft Forums got hit by a Fel Reaver, died, and ended up in The Barrens - which is in Azeroth. Crikey, that was one mighty punch.

That Fel Reaver must have hit him VERY hard indeed. Blizzard poster Eyonix offered an explanation:

Basically, if you're Horde and for any reason the game is unable to identify which graveyard to send your ghost, you'll be ported to Crossroads. It's not necessarily a bug connected with a specific portion of a zone, there are a variety of factors that can cause this type of communication failure.

Fortunately, it's very rare.