There is no "his own farmland". All land in Ireland is owned by Ireland. You don't magically become a sovereign of your own plot just because you have a title d

There is no "his own farmland". All land in Ireland is owned by Ireland. You don't magically become a sovereign of your own plot just because you have a title deed, Ireland still ultimately owns that land. You're just granted most of the rights relating to use of that land. But not all rights. And archeological finds fall in the "not all rights" category.