"Caledonia" is obviously about Scotland. But I always felt the song to be an almost generic sort of homesick song. It's that universality that connects with most listeners, I think. It did with me, though admittedly, I've been around ex-pat Scots my whole life and been listening to Scottish homesick songs and sentiments a long time.
Nobody sings a homesick song like a Scot. Especially one still living at home (see Billy Connolly for elaboration of same).