I would venture to guess Tom. I certainly don't know for sure, but he has a wife (don't know about PJ's marital status) who is herself a founder/CEO and wouldn't raise eyebrows spending time working at the Github offices.
Just last Friday his wife's startup is accepted to Techstars NYC, and she is going to be at NYC. It may be a good timing for Tom to take a leave to be with his wife.
Just guessing here. I could totally be wrong. No offense to Tom; I looked up to him.