That GitHub search only covers the main branch, not the not-yet-merged Rust rewrite; the only Rust code in there is tests for Rust FFI (so that people can write native extension modules for Bun in Rust if they want to).
I have not had time to look at the code myself, but from when this was initially posted to Reddit, IIRC it had around a thousand global mutable variables, which are unsafe to access.
I am very curious what the numbers are once the test suite passes and after a few passes of reducing the amount of unsafe.