I don't think this is true. Rust cannot prevent all possible forms of denial of service, but there are plenty of underlying DoS causes that Rust either outright eliminates (such as memory corruption without further control) or mitigates through stronger types.
A recent example of this is CVE-2024-0567 in GnuTLS: an invariant that otherwise would likely have been noticed at the type level is instead checked with an assert, leading to a remotely trigger-able DoS.
Nor the other myriad of logic and parsing bugs that led to incorrect behavior (more than just denial of service) in the Java library that was somehow not as good as Rust :/.
A recent example of this is CVE-2024-0567 in GnuTLS: an invariant that otherwise would likely have been noticed at the type level is instead checked with an assert, leading to a remotely trigger-able DoS.