The answer here lies in epidemiology and the pathogenic nature of the virus. Humans infected with Ebola have a range of recovery rates of 5-75%, meaning that most of those infected will not survive infection. Given the combination of preparedness factors at first recognizing a true outbreak in Ebola and viral load which had already been spread by the point healthcare workers have organized an efficient response, it is not surprising that some outbreaks are worse than others. I think attempting to correlate the virulence to the type, size with the extent of the viral spread is not pertinent, but rather, as you mentioned breaking "protocol" can have more deleterious effect than simply explaining it by a mutation.
That is not to say that this strain of Ebola is not different from those detected in other outbreaks--in fact it is likely to be quite different and accumulated several mutations.