"Until the 18th century, no one north of the Tweed had ever seen a kilt"

This is misleading. As noted later in the article, highlanders wore plaids, which are basically kilts with an over-the-shoulder piece that can be used as a cloak (it's actually all one big piece of cloth). If you saw a plaid, you'd say, "that's a kilt." Go to a Renaissance Festival and you'll see them all over the place.