Jean-Francois Mezei on Nostr: Your instance only gets a post from another instance if one of your users has ...

Your instance only gets a post from another instance if one of your users has subscribed to someone on that instance. The followed person's posts are thus sent to your instance so you can serve those to your user who followed the remote users. Other reason you would geta foreign post is when soemone on foreign node addresses/mentions one of your users.

So the activity would reflect how many such posts you get from othet instances in the fediverse.