Many countries sell sugar cane, and it can be raised in northern climates aa boutique crop, but I’d guess this was made from molasses derived from sugar beets. (That makes it technically NOT rum in a lot of places, but is likely indistinguishable from the real thing).
Yes I suspected the sugar beet thing. Poland produces a LOT of them. It’s probably safe to say since Lithuania is not too far from Poland it could well be sugar beet rum.