The Scots are represented not as a homogeneous group but as a diverse people, including ethnic differences from Pictish, Celtic, and Viking ancestries. While you may choose to see this as an Othering, it is a step above the kind of racial elisions that tend to happen with Native Americans in films (since that got mentioned.)
Regardless, the original post and subsequent exchanges illustrate nicely what happens when there’s a kernel of truth heaped beneath the crazy, but the crazy emerges triumphant.
Of course, one persons’ serious of ethnic slurs is another’s nationalist myth making. Hence I was not terribly surprised to learn that the National Museum of Scotland has embraced Brave wholeheartedly.
So while McEwan (who, naturally enough, admits to never having seen the film) complains about the stereotyping “Scottish people” as using “silly instruments,” the embedded link makes clear she has bagpipes in mind. Bagpipes, which I hardly consider “silly,” are in Brave. But I first thought, rather naïvely in retrospect, that the discussion was sophisticated enough such that she was referring to the carnyx (the rightmost picture above), which makes a prominent appearance in the film.
In conclusion. Meh.