I got it, but talking to a complete stranger on the phone when you are not looking for a job, so he keeps you in mind for an undefined later? Maybe drop in an e

I got it, but talking to a complete stranger on the phone when you are not looking for a job, so he keeps you in mind for an undefined later? Maybe drop in an example, because I don't see how could it work better than just dropping an email which you either delete (and post an obligatory rage-tweet about stupid recruiters) or tag for later if the offer/company seemed interesting.