Rust for embedded Linux kernels

>My high-level understanding of Rust is that it will refuse to compile when presented with code that could cause memory errors

Yes. But that is only true for Rust code outside of unsafe {} blocks. (All C code essentially is inside of an unsafe block)
Inside of unsafe blocks the unsafe code has to ensure that the requirements of Rust's safe code are upheld.

Therefore, the Rust<->C bindings have to ensure that the requirements on both sides are upheld.
If the C side struct cannot be moved, because for example it contains list_head, the Rust-C-binding needs to pin that structure so the safe Rust code can't move it. If it tries to, it will *then* get a compile error.

But if the C code didn't have list_head before, it was movable and there was no need to pin it. Adding a list_head can therefore break safe Rust code, if the wrapper was not prepared due to the missing pinning.