The article should have said: "by magnetic induction". An AC current driven electromagnet induces a current in the metal, the induced current in the metal also

The article should have said: "by magnetic induction". An AC current driven electromagnet induces a current in the metal, the induced current in the metal also has a magnetic field (basic physics), and it is this magnetic field that is then used to "sort" the conductors (metals) from the non-conductors (non-metals). But then, the article was likely written by someone lacking an engineering/physics background, and so "extracted by magnets" was likely as much as they could comprehend of the process.