I think there are references of the entire world being "Hyrule," but I don't remember where. I do agree, however, that in this case it most likely refers to the Kingdom of Hyrule. It is said to have been left by the Hylians, who we know is a race specific to the Holy Land:
LttP said:
Long before now, a people called the Hylians prospered in this land...
They say that in this country, a few remaining treasures of that people are hidden away...
I've heard that the Master Sword is also one of those, a sword specially forged to oppose those with demonic powers.
Some modification to the story has already occurred in TP with the addition of the sages (when combined with your "I'm pretty sure the Sages are not from Hyrule..." it already contradicts LttP's story), so who's to tell what they'll change in SS? Maybe they'll say that tCitS/Skyloft is part of Hyrule, maybe they'll just 'update' the story, or maybe everything I believe is wrong.
Basically summing it down to either being made by monster or man. And since no monster, besides Gannon of course, has the intelligence to make such a sword, it only points to a man made sword.
Could be a deity or any number of intelligent mythical creatures we have or haven't been introduced to. I'm not really going to continue this conversation much more until we know more about SS. For now, I'll say that occam's razor points slightly toward "man" but again we have no idea the nature of the Sages in SS.
Which all leads me to this conclusion, the MS is the only thing that can defeat Gannon/dorf as long as the arrows are used to negate the affects of the ToP.
What's the point of the arrows in WW? Ganondorf had already lost the ToP by that battle. I think both the MS and Light Arrows are just general anti-evil weapons, the former being more powerful and serving additional purposes (key, time vessel, etc).
Or, the MS original creation has no point at all because the [silver?] arrows are the only thing that can kill Gannon/dorf.
It does seem strange that the people would be told to make a sword that could 'repel' evil when there's also arrows that can kill evil. I'd like to see more backstory for the silver arrows in the future.