exhaust rust

New owner of a 2011 Outback here. Had Lemonsquad do the inspection. Inspector reported minor surface rust, so I bought the car because there were no other problems. Today I (naively, maybe) showed the inspection photos to a buddy who works on cars, and he's worried about the rust. Reading...

I just replaced my rear Catalyic Converter as it’s called. ( one after the Manifold one) I replaced it with an aftermarket Walker 55585 Ultra EPA Certified Catalytic Converter. I know it’s always better to keep original but unfortunately some time ago when replacing the exhaust that rusted out...