Nowhere does the article claim that:

   "formal verification of the code" -> "high integrity system"

Formal verification is simply a method of ensuring your code behaves how you intend.

Now, if you want to formally verify your program can tolerate any number of bits flip on any variables at any moment(s) in time, it will happily test this for you. Unfortunately, assuming presently known software methods, this is an unmeetable specification :)