2004 ranger disc brake issue

I had a safety inspection done on my '04 Ranger and while the mechanic was repacking a bearing on the front right part where the wheel goes and he said the disc brake was too small. I can't quite remember exactly what the problem was but to my knowledge it was something to the effect of the disc brake being too small so not as much of the disc is being affected by the brake pad. So instead of the pad braking on (for example) 3 inches of disc, it's braking on 2 1/2 inches of disc. Has anyone ever heard of this happening? Would there be any telltale signs? I haven't had any problems with my brakes, they stop fine, and they don't really squeal at all.

that makes no sense really can you get any pictures of that