I think someone needs to add a few bits to the history, so it might as well be me. All that follows is well enough known.

The Dal Riada, aka the Scotii, were one of the five tribes of Gaels in Ireland, and they are the original source of many aspects of Scottish highland culture, as they added the highlands to their kingdom. This is why an old term for the highlanders is Erse, which means Irish. To be sure, they developped the kilt in Scotland, but it derives from the Irish brat, which was a cloak. The Irish already wore tartan cloaks by that period, although as someone pointed out tartan was around long before the Gaels brought it to Ireland, much less settled in Scotland.

Everything Matt's article says about Irish kilts is true, as far as it goes. They do derive from Scottish kilts, he just leaves out how those in turn derive from the Irish brat, and how the saffron colour derives from the Irish leine (but from the dye, not from the actual colour, because the fabrics are different). The word leine does translate to shirt in modern Gaelige, but that doesn't mean it was a modern shirt, as you may be liable to arrest if you wear the latter without trews.

And of course, what was not historically accurate in the 19th century has become a part of Irish history simply by the passage of time.

As for being celts or not, this all has to do with the DNA in most people being mainly that of the conquered peoples and not their conquerors. So, yes, the English have mainly celtic DNA, but celtic culture and language were stamped out in most of England and replaced by Germanic culture, but survived to a much greater extent in the 'celtic fringe'.

And there were two types of celts in the history of the British isles, the Britons who came earlier and spread widely, and the Gaels who later came to Ireland and then spread from there into the Scottish highlands and the Isle of Man. There were many other groups who came and went and moved around during the course of history, but those are the most relevant to our discussion.

So, yes it is mainly pipers who wear kilts in Ireland, but they have a history from the 19th c celtic revival, plus they derived from ancient Irish brat (or cloaks) anyway.

As for Irish pipers having been taught by Scots, and Irish war pipes being Scottish pipes with a drone removed, this is because the Irish version had fallen into disuse. Bagpipes are originally of middle eastern origin, anyway, not Irish or Scottish. The Scots added the third drone, but they used to have two there as well, and the only reason Irish bagpipes only have two is that bagpipes fell out of use in Ireland before the addition of the 3rd drone.

I have a feeling of deja vu all over again when it comes to this thread, LOL!