Nope, you are configured properly. It is simply informing the user they are about to give permission to an endpoint/credentials that you setup for users.rust-lang.org.
When clicking Signup with Github
When clicking Authorize Application
I think the user is just getting concerned that it states the application is under your GitHub username. Sites like Discourse and Sitepoint use an Enterprise Name/Account for their Authorization Applications on GitHub to make it sound like a Company is requesting permission instead of a specific user.