"certification" is something that is done to a process that produces a software artifact.
So yes, in some sense it is "particular compiler version." The result of certification says "this compiler will do this when given this, and here is how we ensure that that is true, and here's the process for when that's not true, etc etc etc." Users can then use that specific compiler.
> I.e. basically leading to the same outcome in the end.
The difference is pretty important. Getting this certification does not require that the abstract concept of the Rust language is being specified in any specific way. It does require that a specific inputs to the compiler are described, and because compatibility with upstream Rust is desired, those specific inputs happen to map to inputs to rustc that are identical, but it is important to understand that this can happen completely independently of what the Rust Project decides is best for the language; this is a downstream project.
In theory, if the Rust project wanted a specification, starting with some of the work Ferrocene has done would be an option. But the qualification process doesn't require that.
> Or does this mean to not get the hopes up (right now) for using Rust in a ISO26262 certified project?
The opposite, this means you can use Rust in these places. Even though this work does not specify Rust.