Such laws apply extra-territorially and are imposed not merely upon those born north of the border, I'll have you know. Them Brits even try to claim the likes of my Donegal-born self through my Tyrone-born father, a man who's never held a British passport nor identified as British in his life.
See, it's not just Irish nationality law that has extra-territorial effect; it just combines the principles of jus soli and jus sanguinis when operating in relation to the whole island of Ireland whereas the citizenship laws of most other states apply extra-territorially on a mere jus sanguinis basis.
Congrats to your son, by the way. I'm sure that'll prove a fantastic stepping stone to greater things in the future. If you get my drift. ;)