Interviewing for a job that has most likely been filled

I'll try to keep it short. I've been applying to every relevant job opening that's popped up within my dream company for 6 months (different titles/seniority levels but all within the same area). I either got no replies or standard rejections. By a stroke of luck, I happened to have a mutual connection with someone high-up in the company, who mentioned my name. Now I've been invited to a short interview to see where there might be a fit (for current or future openings). The jobs I applied for have most likely already been filled as they've been taken down. How do I even prepare for this interview?