I think it's an aberration. I know what Green did his first two season's here.. He's almost 29 and I might be wrong but I don't expect him to continue.. Trade him in the off season while his value is high.
Andrew Miller is a player that comes to mind. They both went to the pen full time at 27. Miller took 2 years to really put it together. His first great season was at 29.
If Green gets his walks under control, which I think he will, I could totally see his whip under 1.00.