That code would return exactly the user your orchestration is running under at that precise moment. If your orchestration later dehydrates and is moved to a separate server, then sure, it could rehydrate again and be running in a different host instance and a different account. Don't see what the problem with that is.
The simple fact is, theres no such thing as "the credentials under which the orchestration is running". Orchestrations don't have credentials attached to them, so at best what you can ask for is which credentials the host instance it is currently executing on has associated.