> would you write that you were the author of some open source project

They didn't drift out a message to sea. They wrote it on their handiwork. Would people write their names on their open source project? Yes, they would, and they do. In fact there are licences where the only requirement is that you have to preserve the name of the original authors on the project. This is extremely common.

This is the same. They thought they did a good job, were proud of it and signed it. The same way a painter signs a canvas or the crew writes their name in the credits of a movie.

They used a glass to preserve the paper in an otherwise inhospitable environment.

> Surely you don't think they are actually upset at some people none of us know for not writing a poetic message.

Why would I think they are upset? They are not upset. They are arrogant and demanding. Instead of accepting what it is (people who the history forgot preserving their own name attached to something they put a lot of work into), the commenter is wishing they did something more which would have been more appropriate according to the commenter's values.

> would you write something about your real feelings, the world around you, your thoughts and hopes and dreams, or maybe even share something about your town, your ancestors, your culture, the things you care about, etc.

Did Steven Spielberg wrote any of those into the credits of Jurassic Park? Or just wrote "Director: Steven Spielberg"? This is the same. The message is the lighthouse. The bottle is the signature. It is a "we did this". And they don't have to expound on the "this" because if you found the bottle you are standing in it/on it.