Yeah, this is a strange mix of information being conveyed. Tetanus is indeed caused by an anaerobe, and it’s caused by a puncturing wound. The depth of the wound is what causes the oxygen-free environment. The correlation with iron, from my understanding, is solely because a nail can easily cause such a puncture. A nail stepped on in the general environment can easily innoculate the wound with with the relatively common Clostridium tetani bacteria, which causes tetanus. I don’t think rust is a factor, though I’ve been wrong before.