I would agree that's the case. I think that if we look to the definition of “national emergency”, either paragraph 3(a) or paragraph 3(b) is where that is made clear. It has to be an emergency that's beyond the authority or capacity of a province to deal with it. Second, paragraph 3(b) has to deal with something within federal or national jurisdiction that threatens “the sovereignty, security and territorial integrity of Canada”, writ large.
Could you have a national emergency that is more regional in nature and isn't truly all across the country? I think so, but the issue is that it has to rise to the level of something that is of national concern. That takes it beyond the provincial jurisdiction and concern up to the national level.