I don't know whether WMATA's communication was adequate under the circumstances or not, but in my opinion, it doesn't matter once these passengers take matters into their own hands, put themselves and others at risk of injury or even death, and creating even bigger delays for thousands of other passengers. Clearly there are differing perspectives on what happened, but even if there are breakdowns, that doesn't give people the license to do whatever they feel like.
Washington Post story here: http://www.washingtonpost.com/local/rebellion-on-the-green-line-as-passengers-flee-stalled-metro-train/2012/07/04/gJQA7rk7NW_story.html