adventures in prosopagnosia (maybe)

When I was looking for something at the drug store, I heard some guy in back of me say "hi". My first instinct was to assume he was on his cellphone and ignore him. Then he said it again so I thought that might be a "polite" way of saying, "get out of my way". So I moved. Then he looked at me and said Hi again, so I said hi back. Then he asked "are you off from school?" I just nodded. I was kind of puzzled at this point He didn't really look familiar but his voice sounded like this guy I knew in hi school. Something about hi tone made me think it wasn't him, unless he changed a lot. I don't know whether or not it's sad that I remember voices and tones better then faces. Would it be expected that someone I hadn't seen since hi school would say something like "don't you recognize me? I’m..."? I honestly don't know the answer. Maybe it was somebody I've never seen before making Smalltalk at the drugstore. I don't know how common that is in this age bracket either.