I feel like I disagree. I don't have a "duty" to do anything. If I was able to find the information and make a discovery, then others are capable of it too, and there is a lot of value in allowing people to experience that process on their own. If you ask me, I'll tell you, but I feel leaving the question open for others can often be worth doing.

I think the author makes a far finer point on one of their linked project pages, All About Berlin:

"All About Berlin is my answer to the hastily written SEO spam that pervades the web. It proves that a website can be successful without annoying the everliving crap out of its readers.

It has no ads, no paywalls, no dark patterns, no newsletter pop-up, no coercive cookie notice, no call to action, no comments, no promoted content, and no share buttons. It gives straight, honest answers for free. That’s it."

This is more useful thinking about the core issue, I feel. You don't have a duty to document, but you do have a duty to not intentionally obscure useful information in order to derive a personal benefit from that obscurity. No small irony that this is on a site that designed to take _government_ information and make it more accessible to citizens that have already paid for it.