The mruby VM as used in Artichoke uses Artichoke's Rust implementations of `String`, `Symbol`, and `Array` (and many other core classes, these ones just happen to be used by the VM itself). The symbol table (which is an essential part of how classes and methods and `send` are implemented) is implemented using the `intaglio` crate which is part of the Artichoke project.

These implemented-in-Rust bits expose themselves to the remaining C with `extern "C"` APIs written in Rust that maintain ABI compat with the mruby code they replace.

The mruby VM is getting eaten by the Rust parts, so I don't think it's quite fair to say that Artichoke uses mruby as an off the shelf component. To fully move beyond mruby though to a native Rust VM will take time.