> I thought they were switching most of the kernel and drivers to Rust, for some reason.

Note that zircon itself is not allowed to contain any Rust [0]. It's not exactly specified what they mean by the kernel, but it seems that this includes not just the microkernel but also everything that lives in the zircon top level directory, which is enough to boot the system. tokei says there is not a single line of Rust in that entire directory (but about 1 million lines of C/C++).

[0]: https://fuchsia.googlesource.com/fuchsia/+/cb20372465f875ff4...