That just means you can play with people in a modern online fashion. It's a single player game with competitive features where a large group of people can join a lobby for competitive battling.
Imagine if MHW had it so you could see every single player running around the main encampment in your server. But not so many that you can't see the game. It's gonna be like that.
Well what I get from the trailer, is that is more designed towards being a game that you want to play with others online, doing quests and the like, it has single player, but even that seems more designed towards multiplayer.
Let's have a champion time!