Here are two pictures that will show you the difference between good brakes and bad. When a mechanic says your brake are seized this is what he means. The caliper on the brake that pulls your brake pad onto your rotor and when its rusted out like this it doesnt slide properly and that can cause many issues with your brakes. Here is a pictures of what a good one looks like on the left and what a bad one looks like on the right. your pinion has to be heated up to be able to release some rust for it to come out and that in its self could cause damage.