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“likely to be Pictish, dating back as far as the third century AD.”
Who writes this stuff ??? Bronze and Iron Age are FURTHER back in time (than 200-300 AD), so phrasing it with “back as far as the third century” is badly done — as it implies FURTHER BACK IN TIME rather than less old (as this reported finding).
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Probably by people who assume that the reader is well informed. No doubt that the people who came to be called Picts existed in pre-Roman Britain, but they were not so called until the Romans gave them that name. Since what became the Highlands of Scotland was never occupied by the Romans, the Pictish era coexisted with the Romans and after they left. Without a written record, what little we know about the Picts come from the Romans and from people writing several centuries after the disappearance of the Picts. That's why this discover may be so important.