Instance federation is handled by the Admin of the instance you’re on. This is the first I’ve heard of an app bypassing this. It is an interesting idea. However, the way they were doing the details must have been really complicated.

The Lemmy instances have transporter bots that run in the background between instances. These are configurable to regulate the traffic volume and update rate between instances and user interaction. Instance Admins can disconnect these bots between any instances they do not wish to connect to for various reasons. As of around a year ago (last time I looked into the details), when a community defederates and stops these bots it can’t alter any previously synchronized data. So communities and previous posts/comments will be visible. Due to the lack of any transportation bots, you won’t see any new content posted from the foreign instance. You will see any content posted by yourself or other users to this foreign community from your home instance, and this will look normal from the home instance you posted on. However this data is never synchronized so it is only visible on your home instance. It will not be visible to any other instance regardless of their federation.

For an app to bypass federation like this, the user likely wouldn’t know the underlying functionality of federation and might be interacting in a lot of places where their interactions are not visible to others. The app would need to use a list of the instances and scrape or do something unusual outside of the instance server to bypass how Lemmy was designed as far as I’m aware. Speculatively, maybe that was the thing causing so many server connection issues over the last few months.