I would say that "Iberian" in this context simply means people who originated from the area now occupied by Spain and Portugal.

Whether these people had celtic culture at that time or acquired it later is open to conjecture. The timescales for the Iberian migration from the south and the celtic arrival (suppposedly) from the east are very similar so it could be that this was a method of arrival.

It's interesting as I was certainly under the impression that the celts arrived in Britain through E Europe and germany across the N sea and then on south down the Atlantic coast. This suggests things happened differently.

However the bagpipe is not a scottish specific instrument but is in fact of Middle Eastern origin. It was common throughout europe before the advent of keyboard instruments (with which they cannot harmonise)

keep to the Fen Causeway