I love the statement in that second source that the "Anglo-Saxon and Danish conquests followed in quick succession." That's like saying 'The Black Death swept through Europe in the 1340s and 1350s, and was quickly followed by the rise of Hitler's Third Reich.' ANYWAY.

There's an excellent answer here by /u/Kelpie-Cat all about the Picts and the extent to which they can or can't be considered 'native' to the British Isles.