You don't need to prove it, that was never a requirement. You can simply say it. The only complication is that there's a fair number of people who, for some reason, really want to pass LLM output as their own. They are present on HN too. But here's another ancient trick to overcome that: reputation. Either the reputation you already have, or reputation you build over time. If you have a reputation as an honest person with genuine interest in software, you really don't have to worry, and you will have audience for your work.