fe3+ definitely exists in non-animal matter too. We can talk about quantity, whatever, but my commentary is intended to criticize the baiting and conclusion-drawing.
Fe(III) ions exist in all the cells of all aerobic living beings, for instance in the molecules of the so-called cytochromes, which are used in the cellular respiration.
Nevertheless, the amount of Fe(III) that exists in almost all cells is extremely small in comparison with the amount of Fe(III) that exists in the blood of any vertebrate, where it is used to transport dioxygen in the entire body. The "red" muscles also contain a similar protein to that of the red blood cells, which is used to store dioxygen.
Therefore any kind of food that contains either blood or muscles rich in myoglobin will contain much more Fe(III) than anything else.
It exists at MUCH SMALLER amounts. Their conclusion drawing should be based on an amount should it not? Lead from shooting my gun is not going to damage me the same as eating a bunch of handfulls of pure lead because of the AMOUNT that my body will end up processing. Quantity is so key its absurd to overlook it.
Nevertheless, the amount of Fe(III) that exists in almost all cells is extremely small in comparison with the amount of Fe(III) that exists in the blood of any vertebrate, where it is used to transport dioxygen in the entire body. The "red" muscles also contain a similar protein to that of the red blood cells, which is used to store dioxygen.
Therefore any kind of food that contains either blood or muscles rich in myoglobin will contain much more Fe(III) than anything else.