...substance abusers. (aka "frequent flyers") ERs are a common destination for many of them because of their own choice/doing or because society basically sends them there by everyone passing the buck. Try and figure out an underlying medical problem with the poor wretch I described above. Hint: not easy. And they often have tons of medical problems.
I don't know about this particular instance, but I can tell you homeless men often go to ERs to get a "hot and a cot", distracting staff from true emergencies. ERs btw are not the best care or non-emergent or chronic illnesses. That's best provided by your normal doc. 
Police, for example, have to have a huge knowledge base these days to even give a basic response to the problems they are called for. It is unfair to expect them to be an expert in LE (huge undertaking in its own), plus EMS, mental health and other social services. 
The ER may have made a mistake in this instance, but we need to consider they have likely handled 100s....