My first thought: why not use (and contribute to) StatusNet?
My second thought: who wants to contribute to a PHP project (StatusNet)?
It just seems very knee jerk to start your own so quickly. "I hate Twitter. Hey, use my version of Twitter that's open, but allows you to sign in with Twitter."
Then again, he might have decided that StatusNet has too many dependencies and was looking for something super simple--I don't know.