These alumni interviews are informational only. You should respond, attend, and ask any questions you have. The alum interviewing you may not have attended the school to which you are applying, but you can ask general campus life questions.
If you were to completely ignore the interviewer’s request or not show up for the interview, that would reflect poorly on you as an applicant, but the content of your conversation during the interview will not impact your admission decision.
Hope that answers your question.