Although a Nobel Prize winning author, Knut HansonHamsun was, to put it mildly, pro-German, to the point of being openly pro Nazi during World War II. His views about the British blockade in World War I, or other topics involving Germany, must be viewed in that light. The fact of the matter is that the British blockade did cause a certain amount of starvation in Germany, and he may have conflated that with "starvation in Norway."
As an author, he was also against "realism" and "naturalism," preferring to believe in a "mystic" past. Born in 1859 (but living to 1952, that is, to his nineties), Hamsun was no longer a "young" man during World War I--except possibly in his own mind.
Apparently there was a famine in Sweden and Norway in 1868 when Hamsun was young, so that part may be correct. So it's quite believable that he said the quote attributed to him, given his other biographical data. It just had nothing to do with the British blockade in World War I.