Ah ok, you are checking my ruby lib and now I understand what you are referring to with "channels".

Channel messages are kind 42, currently they are seldom used, a lot of client show only kind 1 (main notes) in the feeds, they don't subscribe to channels ones, so you didn't receive any notification.

Amethyst is the only client I know that formally support channels.

For you use case, while waiting a general better channels' support, perhaps you can just use kind-1 events, they are public as much kind-42 and no one care what flows on the global :)