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A double green triangle is different than that. Observe the first thing in this video: http://www.youtube.com/watch?v=K4jsHLMm198
That is a double GT.
What you saw here was a cute little move, though very tricky. What I believe he did (not entirely positive, its a bit hard to tell) is hop out of the triangle normally, cross his freehand on top, and land on the top string, landing him in a reverse triangle. Its hard, but if you want to learn it, just practice!