My impression is that it is just someone who created a community for each language they could think of. But if programming.dev is a popular instance that is well managed, then sure. But for now, it seems that lemmyrs.org have more users and momentum.
EDIT: On a closer look, it turns out my first impression was quite wrong. programming.dev seem like a quite well managed place, so I do not have anything against using that as a base for rust if that is what the rust community chooses.
If that is the case, then I do not really see the point with this question, since it is far more interesting to know the percentage of Linux developers than what particular distro they use. It becomes a comparison of apples and oranges.