o hai Z of the Girlie.
I don't mean to stir the pot anymore, but honestly I was questioning the same thing.
Usually losing a rear end is a very hard thing to accomplish. I mean, if you put enough diff fluid and used the right kind, I don't understand how you could have messed it up. Your car isn't even that old at all, and these problems are rampant in older cars with tons of wear and tear.
Plus, don't you, personally, usually race from a roll (just going by what I read on IA)? Usually the majority of people who replace their rear end or have problems are
constant, heavy launchers. I'm talking, at the drag strip every weekend, doing it over and over for hours at a time.

And like some people mentioned, your gears are stock... it just seems like some pretty serious damage for some not-at-all-serious conditions.
Sounds kinda sketchy, but if this really happened in the middle of your apartment complex with no real warning, I would definitely have it checked out. The only thing I can think of, if you did replace the fluid correctly, is that the person who owned that car before you, beat on that goat like it owed him money (or like a lonely farmer looking for some lovin'!).
Either way, glad to hear you got a cheap fix that quickly! They are be a *****, cost wise, to replace.