Following talks on Nostr about the official account, here's what I have :

I disabled the welcome message, for now it seems good, but public messages should trigger the send of a private message to the user.
Bonus question : why "hello world" and "hello you", depending of the message ?

BTW, we're able to make difference between public and private messages :

It's interesting to keep both in log, but trigger answers only on private messages.