You mean the Picts remained in the Scottish highlands. You are correct about the Scots coming from Ireland. One thing to note is that before the Danes came in the 8th century there were actually FOUR nations I.e. Ethnic groups in what is now Scotland: you had the picts in the highlands, you had Britons(related to the Welsh ) in Alt Cluith the area around Glasgow that is strathylclyde, you had Angles in the southern lowlands and you had Scots between the first and the latter two. To make it more confusing the angles spoke a version of west Germanic that became Scotch ehule is a separate language from English and quite different from thehighlanders Gaelic
You also had Celts in the south-west pocket of Scotland in Galloway, who were separate from everyone else. The Galldovidians.