I have come across this problem at the store, where the packaging isn't always clear about which it is. You can't make rødgrød with potato flour.Yes Potato Flour is heck of confusing, for me who is not American.
I can find the same thing called Potato starch and sometimes potato flour isnt the same as the clean starch , it is flour made of the whole potato.
So I have to sit down and check orgin of the recipe and check what that area counts as potato flour . It is confusing.