Because the deputies (not full fledged Sherriffs, now)
What the heck are you talking about?
Because the deputies came out afterwards.
According to what I read in that article, the deputies were only called after the armed suspect left the ER.
Since the article states that deputies were actually physically present in another part of the ER when the invasion occured, if the ER staff had bothered to call 911 when the armed suspect first entered the ER, given that the armed suspect was taking the time for a search, the deputies would probably have caught him at the scene.
LawDog