Yes they WERE obliged to say where he came from. Saying nothing makes you part of the farrago of bullshit that gets Dirty Old Town classified as "Irish trad" and encourages Irish (or more often wannabe-Irish) xenophobes to think that sort of racism is just normal and not worth commenting on. If you put out a CD labelled as "Irish music" and a large fraction of what's on it isn't Irish in any way, you have some explaining to do.

It's less common than it used to be, and as Martin Ryan pointed out there's absolutely NO need for it; Irish tradition has plenty enough achievements of its own without stealing the credit from other people. The minority of anti-English knuckle-draggers are a destructive discredit to the Irish music scene.