Not that small, I would say but no, the notification was there, it was published whenever you posted your reply and I saw it via the discourse Android app. Unfortunately, the app doesn’t take you to the post when you tap the android notification so I navigated to meta, tapped my avatar and tapped the notification about your reply. That’s how I got here. But now it’s no longer there:
Oh, this is expected behaviour, I just never noticed it before. If you’re watching a topic, we don’t want you to end up with millions of notifications about a single topic, so we only keep the ‘most recent’ notification.
So after you received the android notification, merefield replied and caused the other notification to be deleted. We don’t delete the notification from Android, only from the web UI.