I interpret it as related to expert-at versus expert-on. If you assume that an expert-on is always an expert-at, then someone explaining something they can't do is clearly not an expert.

I'm not sure that assumption is true, though I could believe it's a useful rule of thumb.

My interpretation is that having an explanation for something is useless if you can't actually make it happen. And even if you don't fully understand how something works, it's good to be able to use it.

For example, I would much rather be able to use a computer than know how it works.

Also, if you can't do it, that calls into question whether your explanation is actually valid. Anyone can explain something, so long as they're not required to actually make the explanation useful.

Think of Steve Jobs vs. the business school professor who wrote a book about entrepreneurship.

I don't know, but it sounds similar to "It's smarter to be lucky than it's lucky to be smart."