Unknown 'Players needed to start' message when loading worlds

When loading some worlds,  there is a very mysterious and ominous message at the bottom of the screen. I have no addons on this world. Maybe it has some thing to do with EDU mode but idk. My worlds are usually singleplayer btw, so I don't know what it's talking about.

The only thing ive done in this world is break and place a few stone blocks, chests and heat blocks and stuff, so no commands apart from /reload. Is it to do with server resource packs? Because I was on a server (the Hive?) like 5 minutes before this, and it contains similar things.