Name: Sandy B. Ford River Twp, Michigan UP (Zone 4b) (Zone 4b-maybe 5a)
I agree that it may not have had enough sunlight; but container-grown potatoes, for the most part, don't seem to produce very well. And, if the plant was still growing it may have produced more if left until it died back.
“Think occasionally of the suffering of which you spare yourself the sight." ~ Albert Schweitzer C/F temp conversion