Announcing an international public health emergency (because this is one) is not the same as announcing a global pandemic emergency (because this isn't one).
I think the phrase "international public health emergency" sounds far more scary that the composite parts.
International? Check. It is completely expected that cases of Ebola will arise in further countries in Africa, particularly those that would naturally host the virus, those most exposed in terms of the movement of people from affected countries and those with more fragile infrastructures/poor sanitation/etc.
This is, as I understand from the various reports, what the WHO mean by "international". As has been outlined here and on other threads, there is nothing to say that in the UK, it would represent a public health emergency, in terms of a massive outbreak/transmission event.
Public health? Check. This outbreak needs to be monitored and controlled at the level of entire populations.
Emergency? Check. Requires immediate action, both to treat and to control.