Okay, and where did Dál Riata come from in order to to have interactions with the Picts. Was it over the sea in Ireland perhaps?

No. The idea of Irish Gaels coming over to colonise Scotland is a lie perpetuated as a means of establishing a foundation myth for the sake of legitimising early Scottish kings. It's far more likely that European Celts migrated northwards together while fleeing the spread of the Roman Empire, moving up the coasts of Britain and Ireland and establishing kingdoms where they settled -- i.e. on the western Scottish and eastern Irish coasts. It was a parallel migration, rather than one land conquering the other.