Neither. When the Romans first occupied Britain, the Picts were speaking a language that was indecipherable to the them. The Romans guessed they were Iberians. The Romans never tried to occupy Scotland, and the Picts eventually picked up the Gaelic language from the “Scots” who got there from Ireland during late Roman times.
Harold, I think you have both items backwards. The Scots traveled to Ireland. Not the reverse. Why do you think The Romans built the Hadrian’s Wall? It was to keep the folks from Scotland from kicking their asses. There is a huge amount of history involved in this area. I suggest you read “Born Fighting” by Jim Webb, (Yeah, the (D) Senator) to get the results of his many years of research of this subject.
If they were Iberian, then they were Celtic.