That's true but I'm not constricting "expert" to just domain expertise. An expert in <whatever_technology> who has worked hard and invested time into acquiring

That's true but I'm not constricting "expert" to just domain expertise. An expert in <whatever_technology> who has worked hard and invested time into acquiring that expertise is often also an "expert" at not being a nuisance in the fields that he's an amateur. He's able to ask quality questions (instead of inviting snarky lmgtfy.com). He's an expert at being a non-expert. Even if Paul Graham doesn't know Rust, I think it's safe to assume that any questions he'd write in an online community would not be ridiculous (is Rust slower than Bash?). Any amateurish observation he'd have, at minimum, would have some intelligent thought behind it.