I thought it was very obvious throughout the video what was happening...

Rust has compile time checks to enforce some safety. In comparison Fil-C is a lot more memory safe, it's more comparable to being a software implementation of CHERI.

Unfortunately it comes with downsides: runtime performance, runtime enforcement, granular safety (the safety is around allocations).

It also comes with huge upsides: you can run C/C++ with little to no code changes. Imagine compiling nginx and the associated system libraries with Fil-C, the performance hit is probably acceptable and now the web server is memory safe.

Rust probably provides enough memory safety (even if it is not complete safety) in most circumstances though.