That's not entirely correct, or at least misleading. Rust will provide the same guarantees for variables in memory shared between processes as for variables in memory shared between threads. But you have to make sure that any locking datastructures you're using (like mutexes or read-write-locks) are able to work across processes.

(There are limits, though: if you map the same physical addresses to different virtual addresses, Rust can't help you. However, that is independent of threads/processes, because you can also do that in single-threaded programs.)