The incident as reported
I do not claim to know a tiny bit of truth about the incident. Rather, the interesting narrative comes from the various accounts in the Thai mass media (newspapers and TV), presumably consumed by millions of Thais, and from the communications among the Facebook community. No matter how true these accounts are, they reveal how the Reds and their protest are seen and conceptualized by those media and the Facebook community.
The media reports, especially on TV, are full of horrible eyewitness accounts. Doctors, nurses, patients, and their relatives are panicked. They frantically moved patients, many of whom are in a serious condition and should not be moved, to another building. What is shown on TV is not an orderly operation as precaution but a chaotic, disorganized action by medical personnel who were in fright! The Reds are coming! They heard the Reds are coming! People said the Reds are coming!
There is no need for a single picture or photo if the Reds were armed, or a report of a single shot, but the public assume that the Reds stormed into the hospital fully armed, threatening doctors and patients with weapons, causing horrific chaos as people tried to escape the armed invasion. A nurse was reported saying that she has to work with fear of bullets from the Reds everyday, as if there were a shot at the hospital even once. (Finally there was, in the parking area of the hospital when the UDD group actually encountered a few army officers. The soldiers shot at them. The UDD people escaped uninjured.)