It isn't unrelated, it is entirely the point. The Irish don't have their own currency, when you don't have your own currency you don't ultimately control your own affairs you share them with the others who use that currency.
> you don't ultimately control your own affairs you share them with the others who use that currency
The currency had nothing to do with it. The only thing which would have absolutely forced them to stand over it would have been existing EU law - which there was none.
The European Central Bank can't legally stop issuing currency to Ireland just because some French or German banks got burnt.
If a bunch of German/French banks suddenly get 40billion in losses what happens next? They will have to panic sell their remaining good assets to remain solvent, that transmits the problem on to the other banks that they have invested in. Because the EU banks all tended to lend money to each other.
So you end up with the problem transmitting around europe (and beyond) but it's worse because everyone is trying to sell everything at the same time to remain solvent.