If the guy doesn't know how he does it, what he has to say will not be very illuminating. To be able to teach, you have to understand why you are doing things the way you are doing them. It's surprising how many people are good at what they do, but still don't know why they do things a certain way, have not considered other ways and noticeably slow down when they leave their comfort zone.
Wow. What a strange advice. All it takes to be an expert on anything is labeling yourself as such. I'm an expert on a lot of things.
Being competent at something, on the contrary, means actually going there, doing the stuff and learning the craft.
If the guy trying to teach me mechanics doesn't have dirty hands and nails, I'm not very interested in what he has to say.