I am also not a chemist. A (bronstead) acid is a proton donor. An atom that donates a proton becomes an (an)ion. The acid is not the anion; the anion is the

I am also not a chemist. A (bronstead) acid is a proton donor. An atom that donates a proton becomes an (an)ion. The acid is not the anion; the anion is the conjugate base of the acid. Not all acids form an anion; hydronium is an ion that becomes neutral when it donates a proton. I do not know why the article used the term ion here. I am guessing it is because the abstract refers to IP6 as a polyanion. It is not referred to as an acid, because it is not participating in acid/base chemistry (though I tried reading the paper and the mechanism is well over my head).