Did you read what they wrote? Their point is that doing a fresh rewrite of old code in any language will often inherently fix some old issues - including memory safety ones.

Because it's a re-write, you already know all the requirements. You know what works and what doesn't. You know what kind of data should be laid out and how to do it.

Because of that, a fresh re-write will often erase bugs (including memory ones) that were present originally.