Think of it like email. Email is a protocol that people can use, but email isn’t “owned” by anything. Instead, different mail servers (like outlook, Gmail, proton, etc) use that protocol to talk to each other.
Lemmy uses a protocol called activity pub, and different instances like lemmy.world, lemmy.ml, etc can all talk to each other using that protocol.
You’re on the instance sh.itjust.works, while I’m on lemmy.xylight.dev, but you can still see my comment!