I see this so often.

That is not what is meant. No one is taking the "no true vegan would eat vegetables fertilized with animal byproducts" position here.

1. Bad actors are not a reason not to enforce a community rule. If I start a forum for victims of sexual violence and state, as a community rule, that people who have ever committed sexual violence are not permitted, how do I enforce that? The answer is "to the best of my abilities."
2. The bar for No-AI is not "this has literally never even been ingested by an LLM, nor has any of its components, nor has anything like any of its components." In the vast majority of cases what myself and others are looking for is that, to the maximum extent possible, you did not seek out LLM assistance on this project and barring that 100% of the content is your own creation and not the output of an LLM.

While I can't speak to this project's values specifically I can say for me, it is enough to know that every word of prose or line of code followed the same path

Your brain -> your hands -> that project

Your project was added because it matched the criteria for addition, that projects publicly state it won't be using any AI, in your case you mention "strictly forbidden".

To answer some of your other question, noailist.org has to rely on some trust with project owners that they are "to the best of their ability" enforcing their own AI policy. There is a lot of trust involved, from the project owner and from a project's contributors.

Some projects have been removed for not enforcing their AI policy, but they have been blatant and public about not following their own policy. Some projects the public have reviewed the submissions and found clues there were AI leveraged submissions, and the project was removed until it can follow its own public policy.

In your example, Sam might use LLM to find an answer, and then contribute some of their own hand written code. In this case this means Sam is still using AI and ignoring the societal cost of AI being too high ( https://noailist.org/why-no-ai/ ) by continuing to use AI at some point in the process.

If Sam admits to leveraging AI, you as the project owner may decide to bar Sam from further submissions unless they agree not to use AI anymore. That would be enforcing your AI policy to the best of your ability.

It would be dishonest if submissions were made with the use of AI without the project owner knowing about it especially having a public No-AI policy visible.

This may be a concern from project owners that contributors are submitting additions while leveraging AI but not being visible or honest about it. noailist.org would have to trust that project owners are attempting to find out if their contributors are leveraging AI or not... and being strict about enforcing their policy, and there are some tools and signs that help identify AI additions.

There might not be much leeway if noailist.org or the public is reviewing a project and the project owner had no idea that contributors were leveraging AI, the project would probably need to post a public statement to its contributors, and do more to enforce its strict No-AI policy. The project would probably be removed from noailist.org until there is more done to enforce the policy strictly.