Unfortunately, as is most always the case of negligence instead of some particular language features:
“A commission attributed the primary cause to general poor software design and development practices rather than single-out specific coding errors. In particular, the software was designed so that it was realistically impossible to test it in a clean automated way.“
You sound like you make a refutation, but you really don't. This whole discussion is about giving tools to developers that are systematically less error-prone, which your quote suggests would have been helpful to that specific development team.
https://en.m.wikipedia.org/wiki/Therac-25