Are there people today who claim Pictish heritage?
The ancestors of the Scots invaded and colonized from Ireland, and the Pictish population was subsumed into a probably numerically greater population. Pictish literacy vanished.
Not long after, the Vikings swarmed over the British Isles. Among people with British or mostly-British roots, it's not surprising to find in excess of 30 percent Scandinavian DNA even where there's no genealogical records to support it. I've got known Scottish (great-gma) and Irish (great-great-gms) roots, and I still have more Scandinavian DNA. :^)