Hmm, how does that one work ?
Instances report the latest activity ID through a public API endpoint. This compares the latest across instances. I can’t remember the details, but one thing to remember is that not every instance gets every activity so it’s not 100% accurate.
The way federation works is that you subscribe to a community, then that community starts sending your instance new content from the community posted after you subscribe.
If you have no subscribers, then you have no federation.
Check out https://lemmy-federate.com/ for getting federation started. This lets you enter a community and instances that have signed up will have a special account subscribe which causes your community to start sending content to their instance.
You can also post in special lemmy communities for letting people know about your new community.
Hopefully this is all the issue is! Have you tried using your account on your instance for commenting on other instances, e.g. replying to me here?
I think PieFed has only recently got an API for apps to connect to, hence the surge.