They're wrong. Ireland and England were fighting at that point in history for Irish Independence (Scotland too, but who cares ^_^ Kidding, kidding), but that wasn't part of the Hundred Years War.

Though, I can see where they got confused, I guess. Since the Hundred Years War is a series of wars, and there were a bunch of battles in that time period in Ireland. But I'm fairly certain only the ones between England and France would count as HYW battles.