To be clear, @dang does a lot! His moderation is a big part of why HN is such a useful forum. But you're right that the text '@dang' being posted in an HN comment does not result in the software sending a notification to him.

I have always seen people using @dang and honestly it has always worked, he even thanks me sometimes.

There are regular comments by him, every few days, asking people not to rely on @dang. https://news.ycombinator.com/item?id=39662522

That's random. If you want better-than-random message delivery you need [email protected].