Not just within the EU, any AY operated flights including long-haul.
Are you sure, have you tested? I am 200% sure that this applied in the past only for EU flights, and it was mentioned at Finnair Plus pages, but now I went in to double-check and found this :
or a two-for-the-price-of-one Classic award flights in Economy Class. With this you can purchase award flights for two people from the Finnair Plus service centre but pay the point cost of an award flight for one person. Two-for-one Classic awards are only available for scheduled one-way and return flights operated by Finnair or Norra and must be purchased using points only.
i.e. it does not say anything about EU or longhaul flights. Now this benefit suddenly became very interesting for me.