The metric used by Stack Overflow is "% of developers who are developing with the language or technology and have expressed interest in continuing to develop with it", so it seems likely to me are likely to have some understanding of what writing Rust code is like.

You seem to equate "actual professional" with "meaningful complexity" or "deployed to production", which seems limited. I'm pretty sure I've written meaningfully complex code outside my day job -- and I would guess many open source developers write such code outside the context of their job.