Arguably, someone in that position speaking so definitively while also being uninformed, is at least a little "toxic."

I'd say toxic. When you point out that "nobody has done this" in this way, there is a strong implication that it's not possible, not reasonable, or not wort the effort.

Rust explicitly aims to be a systems language. It explicitly challenges C and C++ on their own turf. Implying that it's not suitable for serious systems work is insulting.

> Note that the email conversation was from a few years ago.

Remember that the project he said didn't exist was 4 years older than his email. And if I understand other comments correctly, that project was well known among Rust practitioners.

He made strong claims outside his area of expertise. An easy mistake to make, but one that has consequences when you're this famous. Such mistakes are totally fine in private, but in public… they're a little toxic.