I wonder if the difference in reaction between Beloit Piper and Slohairt was the type of kilt they were wearing. If the former were wearing tartan, then I imagine that might be assumed to be Scottish, given that most people can't tell one tartan from another, whereas saffron is clearly intended to be Irish, just as, for example, a solid green kilt would obviously be Irish. Irish tartans are mostly recent, and mostly worn by Irish Americans.

As for the piper comment, much as Slohairt observed, that would be a common comment almost anywhere, except perhaps Scotland. Pipe bands are the most commonly seen kilt wearers in Ireland. I'm told that Riverdance pretty much killed off kilts in Irish dancing.

The comments re Dublin make sense too. You can wear almost anything in large cities without getting much reaction.