The problem with recreating cryptographic libraries is that unless you are a cybersecurity expert, you are very likely to leave hidden vulnerabilities in your implementation.

The author has completely misunderstood the advice to "not reinvent the wheel". Or they're just being needlessly literal in their interpretation.

If your job isn't making wheels, then you use somebody else's wheels when you need wheels, so long as those wheels do what you need them to do for a cost that is acceptable.

There is a high cost to reinventing things. So you don't tend do so unless there is a compelling reason to do so.

If you're just exploring and learning nobody will tell you not to.

Rewrite in Rust is not harmful.