The [[ https://secure.phabricator.com/book/phabdev/article/chatbot/ | IRC bot documentation ]] says "PhabricatorBotFeedNotificationHandler This handler posts notifications about changes to revisions to the channels listed in notification.channels."
It posts notifications to all channels joined instead.
The offending line appears to be https://secure.phabricator.com/diffusion/P/browse/master/src/infrastructure/daemon/bot/handler/PhabricatorBotFeedNotificationHandler.php;9e0f70e17d563972854be77e935cbabf6a3226f1$164