The discussion I started was never about being an expert of something, just having a basic understanding. You chose to inflate having an understanding of an idea to being an expert.

I’ve also discussed cases where the expert level execution requires a lot of non verbal skills, but those experts can still describe the basic underpinnings of what they are doing.

However, unless someone has a severe communication disability, they should be able to communicate the basics of their knowledge. If they can’t explain it, maybe they don’t understand it enough to grasp the science behind why things are the way they are.

If you want to use cooking for example, a cook might understand how to use a recipe without understanding why the recipe requires certain ingredients or techniques. A cook could understand how to make a béchemel sauce without understanding what an emulsion is, what chemical reactions cause a successful emulsion, and which flavors propagate well in that kind of sauce. Being able to cook a béchemel sauce doesn’t mean you understand what a béchemel sauce is.