Hmmmm , well if the early Scots weren't Irish, the Irish did a good job of fooling the Romans who were on the scene in their day and who named the Irish 'Scotti'- that was only later transferred to Scotland. And from the Norman invasion until about the mid-nineteenth century, Scottish Highlanders themselves were referred to as "the Irish" by their Lowland neighbours.

And then of course there are the very ancient Ulster Cycle of tales which have the likes of the Sons Of Uisnech taking Deirdre and invading and settling in present-day Scotland....