A lot of things that C will let you do (even if you enter the realm of undefined behaviour) will simply not compile to C. As the author states, there are semantic differences between pointers and Rust's references.

C pointers can have as many owners as you want, may be subjected to mathematical operations, and can be cast to any type without even an error message. The compiler will just assume you know what you're doing. If you enable enough compiler warnings, it might warn you, but C compilers don't generate a lot of those by default.

Rust will let you only generate one mutable (exclusive) reference at a time. This means straight C to Rust ports simply don't compile.

By switching to pointers, which work pretty much like their C equivalent, you can port the code much easier, but you do of course lose the benefits of Rust's safety mechanisms, because most pointer operations throw away all the safety guarantee that Rust provides.