Well, that, and I think he also answered the question earlier on in the interview where he said that, with the Astonishing, he felt like he didn't really have time to write "good" drum parts the way he wanted. There was a very short window in which he was introduced to the songs, improvised parts, and recorded them. So, if he isn't really satisfied with his drum parts on a 3-hour piece of music, it isn't surprising that he is happier playing other music where he feels the drumming is more complete.