I didn't go to this link. I watched the footage a fellow cyclist recorded that you can find on the VeloNews website and read what he had to say. He said that when they pinned his arm back (and probably when they did the lifting in the photo above but that is my speculation) he heard a very audible snap and the arm immediately went to an unnatural angle. I'm also guessing that photo was lifted from that cyclist's video.
Breaking someone's arm for riding into a park without paying? That doesn't qualify as excessive force?
Ben