“We explicitly build ambitious things, ship quickly, and improve with time. Moving fast is the optimal tradeoff for the kinds of games we make nowadays,” Epic’s Markman said, adding that “it’s a different approach than Epic in the single-player eras of Unreal Tournament and Gears of War.”
Those are two terrible examples to use for single player games.
My guess, and it’s a personal pet peeve of mine, is that it’s the term that people use to refer to anything that isn’t live service. In this case in particular, it’s a perfect example of how stupid it is for that to be the term we use for that. While both can be played with only one player (so can Fortnite), they were both marketed as games that you would be playing primarily multiplayer.