They're ALL branches of philosophy, mate.
I've never actually studied Singer directly or fully so I have no more than incidental knowledge of his positions, but he is somewhat like Radar, in that, having settled on some principles he builds on them exactly as logic dictates, but never then considers a reductio ad absurdum of his own position, because he is already sold on the principles and the numerous apparent successes along the way.
I think Smooth is unfair to him, and I could argue about his philosophy, but I only do that for money. And it isn't really my field, I'm more into metaphysics.