Tartan is supposed to be a new invention (17th - 18th century) created by the Scots and given a false pedigree. Its existence elsewhere and in even earlier times suggests that it may not be Scottish at all, but that it is genuinely ancient as opposed to being a modern romantic invention.
Urumchi mummies, apparently non-Chinese remains in China... Silk Road... tartan cloth and ginger hair... the inference is that Celts were doing business way over yonder.