I think it is reasonable to conclude some iron absorption, but not enough to manage anemia. The anemia from menses or malnutrition or parasites requires pharmacologic dosing and the amounts noted are small. The theory of absorption of minerals from cookware is reasonable and objectively noted. A simple search on PubMed shows a few references including the one noted. A good one noted meaningful increase in hemoglobin in using soapstone. Nickel is known to be absorbed from stainless steel cookware under acid conditions. This could have been a meaningful source of iron, and there is some bioavailability, but i am not convinced it is enough to manage anemia. In modern times we routinely find women anemic despite plentiful food sources of iron.
Agreed however clearly it is enough to make a difference in serum levels even with parasites, which I hope to avoid all days. If a modern person in te western world is anemic it is through willful mal-nutrition. I'm less concerned with today & more concerned with the tomorrows. I well be expanding my cast iron cooking equipement the three pans I have being clearly not enough.