Nothing is ever simple:
The Scots were Gaels who spoke Gaelic, not Scots, and they came from Ireland. It was the Romans who called them Scottie. The Scots language derives from the Saxons who came from Germany and Holland. The Saxons cousins the Angles, also from Germany spoke the same language and gave their name to England. Their language came to be known as Anglo-Saxon and from it derived both English and Scots. Therefore they are sibling languages, neither being a dialect derived from the other. It could be argued that both are German dialects. Clear as mud?? :-}
      Sandy