For me it is the fact that our blood contains iron. I earlier used to believe the word stood for some ‘organic element’ since I couldn’t accept we had metal flowing through our supposed carbon-based bodies, till I realized that is where the taste and smell of blood comes from.
From Wikipedia on bones:
So the statement is a bit faulty, not only because of the relative low amount of calcium in our bones, but also because it appears as a mineral. We distinguish between salts and metals because of their chemical properties being quite different (solubility, reflectiveness, electrical conductivity, maleability and so on).
Edit: I do realize the point of the comment was not to be entirely factual, so if I am allowed as well I would say science is pretty metal.
Thanks for the reality injection!
The statement was glib but even the partial truth of it made me wonder when I first learned it.