So it's presumed that it was 'a telephone call'

If the person came in to see his/her boss, the visitor should have an appointment. But with the (rude)answer OP got, its either he (Boss) don't know/expecting anyone.

Still, same procedure applies, screen the visitor if he has an appointment or just walked in to see the Manager of the company.

believe you me, I myself receive calls, visitors claiming they know my boss (when they don't) and I made a couple of mistakes myself. :)