It sounds serious and strict, but it applies to content that's 'clearly labelled as LLM-generated'. So what about content that isn't as clear? I don't know what to make of it.
My guess is that the serious tone is to avoid any possible legal issues that may arise from the inadvertent inclusion of AI-generated code. But the general motivation might be to avoid wasting the maintainers' time on reviewing confusing and sloppy submissions that are made using the lazy use of AI (as opposed finely guided and well reviewed AI code).