Google shows me that Twitter was founded nine months before Alex came on board. I've read plenty of his posts and presentations and I respect his technical abilities, but your "built Twitter" comment oversimplifies his involvement in the company's history.
His presentations do imply that he was the driving force behind the Scala adoption for their messaging queue, so that's arguably a must-have to reach Twitter's current scale.
His presentations do imply that he was the driving force behind the Scala adoption for their messaging queue, so that's arguably a must-have to reach Twitter's current scale.