You left out the full argument (to be clear, I don't agree with the author, but in order to disagree with him you have to quote the full argument):

The author is arguing that the main reason rewriting a C++ codebase in Rust makes it more memory-safe is not because it was done in Rust, but because it benefits from lessons learned and knowledge about the mistakes done during the first iteration. He acknowledges Rust will also play a part, but that it's minor compared to the "lessons learned" factor.

I'm not sure I buy the argument, though. I think rewrites usually introduce new bugs into the codebase, and if it's not the exact same team doing the rewrite, then they may not be familiar with decisions made during the first version. So the second version could have as many flaws, or worse.