I also don't even know if it's really true. Sure, maybe it's not coherent enough that a person understands it, but if an LLM wrote it, you can be ~99% certain (in my experience) that that LLM will understand it, and usually in less than the time it took to write it. And unlike humans, the LLMs don't die and take their knowledge with them, or change companies, or get ornery when you ask them to explain.
Also, in my experience, Claude doesn't really do what the parent is saying and dive head-first into complex problems and bork your code. It is fairly humble in the face of complexity. It constantly recommends breaking down larger problems into smaller ones that are more easy to grok.
But most importantly, anyone who's a decently skilled software engineer and who's using LLMs to write code is going to be thoughtful. Especially when they're writing code that's important. Unless you're an AI researcher pushing the bounds of what LLMs can do, which let's face it, the vast majority of programmers are not, it's almost always the case that you'll have your LLM writing intelligible code that you can understand and have it explain easily enough.