Listen again:WERE you good at school? WAS I good at school?
Listen to the music of English: Record and compare: Interviewer: WERE you good at school? Gary: WAS I good at school?
Why the emphasis on was? Because Gary was a teacher and he is a teacher now (Past AND Present tenses). He has not stopped teaching! Because he STILL teaches. He has taught for 39 years (Present Perfect).
Gary does not answer the question. He questions the question.