Since liftoff support different instances , you can see a community from a different instance and not the one you are sign in. When it gives you the option to see via my instance it means it will load it from the instance you are sign in or the one you choose. Sometimes content will show up and sometimes no content will be available this last part happens when no one else in your instance have subscribed to it and its not federated.
I hope this helps you to understand!