I must admit to being somewhat confused by the article's claim that Rust and C++ emit bytecode. To my knowledge, neither do (unless they're both targeting WASM?) - is there something I'm missing or is the author just using the wrong words?

EDIT: bramhaag pointed out the error of my ways. Thanks bramhaag!

By 'Rust compiler' and 'C++ compiler', they refer to the LibJS bytecode generator implemented in those languages. This is about the generated JS bytecode.

They're referring to LibJS's bytecode (the internal instruction stream of Ladybird’s JS engine), not to Rust/CPP output formats.