I'm not familiar with Thumbs Carlyle, but he may very well have played the same way as this busker.

I didn't really look too closely at his setup, but I don't think I saw any string dampeners (mind you, I'm not really sure what those would look like anyways). Come to think of it, I think he just let the open strings ring. He said that he had invented the technique 12 years ago, while he was fooling around on his guitar while on the phone. I would have bought the CD, but he said it was pretty New Age, and I'm really not into that kind of thing.